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Changes in T Cell Subpopulations in Lead Workers
ENVIRONMENTAL RESEARCH, SECTION A ARTICLE NO.
76, 61–64 (1998)
ER973790
Changes in T Cell Subpopulations in Lead Workers1 Fumihiro Sata,*,2 Shunichi Araki,* Takeshi Tanigawa,*,3 Yoko Morita,*,4 Susumu Sakurai,† Akinori Nakata,*,4 and Naochika Katsuno* *Department of Public Health, Faculty of Medicine, University of Tokyo, and †Clinical Laboratory, University of Tokyo Hospital, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan Received October 14, 1996
impairments of lymphocytes have been observed (Cohen et al., 1989; Fischbein et al., 1993a,b; Sata et al., 1997a,b). Antigen receptors on the surface of T lymphocytes are associated with small integral membrane proteins called CD3 complexes. Utilizing anti-CD4 and anti-CD8 monoclonal antibodies, it has been possible to divide T lymphocytes into CD4+ helper/ inducer and CD8+ suppressor/cytotoxic cells. From a differential point of view, CD3+ cells and CD4+ cells can be divided into two subpopulations, using antiCD45RA and anti-CD45RO or anti-CD29 monoclonal antibodies (Sanders et al., 1988; Clement, 1992). The subpopulations of CD4+ cells using those monoclonal antibodies had been called ‘‘suppressorinducer’’ and ‘‘helper-inducer’’ T cells because of their functional aspect. However, it is now generally believed that such a subdivision of CD4+ cells is associated with a differentiation stage rather than a functional subset (Sanders et al., 1988).
To investigate the effects of lead on the human immune system, we analyzed T cell subpopulations and B (CD19+) cells in peripheral blood in 71 male lead workers. They were engaged in manufacturing lead stearate in a chemical factory, aged 20 to 74 (mean 48) years. Their blood lead concentrations (PbB) were between 7 and 50 (mean 19) mg/dl. The control group consisted of 28 ‘‘healthy’’ male volunteers without a history of occupational exposure to lead or other hazardous substances, aged 33 to 67 (mean 55) years. In comparison with the controls, a significant reduction in the number of CD3+CD45RO+ (memory T) cells and a significant expansion in the percentage of CD8+ cells in the lead workers were found. There was a significant positive correlation between the percentage of CD3+CD45RA+ (naive T) cells and PbB in the lead workers. It is suggested that CD45RO+ memory T cells may be most susceptible to the effects of lead on T cell subpopulations. © 1998 Academic Press Key Words: lymphocyte subpopulations; lead; memory T cells; CD45RO antigen; T cell differentiation.
MATERIALS AND METHODS
Subjects The 71 male subjects were lead workers engaged in manufacturing lead stearate in a chemical factory. The control group consisted of 28 ‘‘healthy’’ male volunteers working at another chemical factory as security service or clerical works without a history of occupational exposure to lead or other hazardous substances. The demographics of the lead workers and the controls are shown in Table 1. The lead workers’ blood lead concentrations (PbB) were between 7 and 50 (mean 19) mg/dl, whereas their past PbB had been higher as a whole. Currently, a limit of 10 mg/dl (4.9 mg/dl) is considered the upper limit for healthy Japanese men (Watanabe et al., 1985). No subject had signs and symptoms indicative of infection at the time of the study; none had used drugs that could affect immunological analysis.
INTRODUCTION
It has been reported that lead influences the immune system both in animal models and in human subjects. In lead workers, phenotypic aberrations of T cells and natural killer (NK) cells and functional 1 This study was partly supported by Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture in Japan and conducted with all the subjects’ informed consent. 2 To whom correspondence should be addressed: National Cancer Institute, National Institutes of Health, Building 37, Room 3E24, Bethesda, MD 20892. Fax: +1-301-496-8419. 3 Present address: Institute of Community Medicine, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305, Japan. 4 Present address: National Institute of Industrial Health, 621-1 Nagao, Tama-ku, Kawasaki, Kanagawa 214, Japan.
61 0013-9351/98 $25.00 Copyright © 1998 by Academic Press All rights of reproduction in any form reserved.
62
SATA ET AL.
TABLE 1 Demographic Characteristics of 71 Male Lead Workers and 28 Healthy Controlsa Characteristic Age 20–29 30–39 40–49 50–59 ù60 Current smokers ø20 cigarettes/day >20 cigarettes/day Current nonsmokers Exsmokers Never-smokers Blood lead concentration (mg/dl) <10 10–20 20–30 ù30 a b
Lead workers
Controls
5 (7) 13 (18) 19 (27) 25 (35) 9 (13) 42 (59) 28 (39) 14 (20) 29 (41) 21 (30) 8 (11)
0 2 (7) 2 (7) 17 (61) 7 (25) 9 (32) 5 (18) 4 (14) 19 (68) 9 (32) 10 (36)
6 (8) 36 (51) 22 (31) 7 (10)
—b — — —
Number and percentage in parentheses. Not measured.
The procedure was fully explained to all the subjects and this study was conducted with their informed consent. Collection of Blood Samples and Analysis Peripheral blood samples were taken from each individual by venipuncture using ethylenediaminetetraacetic acid (K2-EDTA) as an anticoagulant for measurement of leukocyte count and for immunofluorescence staining and heparin for measurement of PbB. Immunological analysis was conducted within 10 h after the blood samples were collected. All samples were transported and handled at room temperature (15–20°C). The lymphocyte subpopulations were measured using the following pairs of monoclonal antibodies: anti-Leu4 (CD3)/anti-Leu12 (CD19), anti-Leu4/antiLeu45RO (CD45RO), anti-Leu18 (CD45RA, equivalent to 2H4)/anti-Leu4, anti-Leu3 (CD4)/anti-Leu2 (CD8), anti-4B4 (CD29)/anti-Leu3, anti-Leu18/antiLeu3, and mouse IgG1/mouse IgG2a as a negative control (Sata et al., 1997b; Sung et al., 1995). PbB levels were measured by polarized Zeeman atomic absorption spectrophotometry (Z-8100, Hitachi, Tokyo) after 10-fold dilution with 1% ammonium phosphate and 1% Triton X solution. Statistical Methods Differences in age and smoking (numbers of cigarettes smoked per day) between the lead workers
and the controls were statistically significant (P < 0.01 and P < 0.05, respectively; independent t test). Differences in numbers (per mm3 whole blood) and percentages of each lymphocyte subpopulation between the lead workers and the controls were analyzed by analysis of covariance with age and smoking as covariates. The associations between the numbers or percentages of lymphocyte subpopulations and PbB in the lead workers were analyzed by Pearson’s correlation coefficient. Multiple regression analysis was used to identify the model of variables such as exposure of lead (1 in the lead workers and 0 in the controls), smoking, and age which most predicted each lymphocyte subpopulation. All analyses were conducted using SPSS software for Macintosh (SPSS Inc., Chicago, IL). RESULTS
The numbers and percentages of T cell subpopulations and B (CD19+) cells in the lead workers and the controls are shown in Table 2. In comparison with the controls, a significant reduction in the number of CD3+CD45RO+ cells and a significant TABLE 2 Numbers (per mm3 Whole Blood) and Percentages of Lymphocyte Subpopulations in 71 Lead Workers and in 28 Healthy Controlsa Lymphocytes CD3+ cells Number Percentage CD3+CD45RO+ cells Number Percentage CD3+CD45RA+ cells Number Percentage CD4+ cells Number Percentage CD4+CD29+ cells Number Percentage CD4+CD45RA+ cells Number Percentage CD8+ cells Number Percentage CD4/CD8 CD19+ cells Number Percentage
Lead workers
Controls
1570 (570) 60 (11)
1550 (440) 59 (10)
740 (310)* 29 (10)
850 (450) 32 (11)
800 (420) 31 (12)
790 (360) 30 (13)
910 (430) 34 (10)
840 (290) 32 (8)
570 (260) 22 (8)
550 (250) 20 (6)
390 (320) 14 (8)
400 (210) 16 (8)
970 (350) 38 (9)* 1.0 (0.8)
890 (270) 34 (7) 1.0 (0.4)
300 (210) 11 (6)
320 (190) 12 (5)
a Mean and standard deviation in parentheses. * P < 0.05 (analysis of covariance with age and smoking as covariates, compared with the controls).
63
T CELL SUBPOPULATIONS IN LEAD WORKERS
expansion in the percentage of CD8+ cells in the lead workers were found. There was a significant positive correlation between the percentage of CD3+CD45RA+ cells and PbB in the lead workers (P < 0.05). In multiple regression analysis, there was also a significant relationship between the number of CD3+CD45RO+ cells and exposure to lead; regression coefficient (B) and standard error (SE) are −172.4 (P < 0.05) and 79.4, respectively. DISCUSSION
In the present study, we have shown a selective decrease in the number of CD3+CD45RO+ cells in peripheral blood in the lead workers compared with the controls. We have also found that there was a dose-related increase in the percentage of CD3+CD45RA+ cells in the lead workers. Those changes seemed to be associated with each other. Among the membrane antigens that are differentially expressed by reciprocal human T cell subpopulations are the CD45RA and CD45RO isoforms of the common leukocyte antigen family, which have been hypothesized to identify ‘‘naive’’ and ‘‘memory’’ T cells, respectively (Clement, 1992). Memory T cells differ from naive T cells in that they have been activated (typically by antigen) at some time after export from thymus (Sanders et al., 1988). On the other hand, it has been suggested that the adverse effect of lead might be due to its high affinity for the T cell receptor (TCR) interfering with antigen processing from monocytes to T lymphocytes (Fischbein et al., 1993b). There is a possibility that lead may inhibit T cells from being activated or coexpressing CD45RO antigen in T cell differentiation or maturation on account of its high affinity for TCR. Memory T cells preferentially migrate through peripheral organs such as the skin, whereas naive T cells migrate through organized lymphoid organs such as lymph nodes (Mackay, 1991). It has been suggested that normal homing patterns of lymphocytes might be altered by exposure to lead (Faith et al., 1979). There is another possibility that lead may allow CD45RO+ T cells to migrate through peripheral organs more preferentially. We could not detect any significant changes in the numbers and percentages of CD4+ cells and their subpopulations in the lead workers. However, those observations suggested that a reduction in memory T cells in the lead workers might occur mainly in memory CD8+ cells. Similar observations were found in patients with multiple sclerosis and such changes could indicate a defective differentiation into mature CD8+ cells (Svenningsson et al., 1995).
A possibility that lead might be associated with autoimmune diseases has been proposed (McCabe and Lawrence, 1990). However, the association between exposure to lead and autoimmunity remains unclear. On the other hand, increased concanavalin Ainduced suppressor cell activity in lead workers has been reported (Cohen et al., 1989). Further studies are needed to define whether CD8+CD45RO+ cells decrease actually and whether such a decrease, if it occurs, represents a decrease of cells with primarily suppressor or cytotoxic functions. It has been possible to subdivide CD8+ cells functionally into the suppressor cells and the cytotoxic effector cells, utilizing anti-CD11b and anti-CD11a monoclonal antibodies (Landay et al., 1983; Morimoto et al., 1987). Recently, subdivision with anti-CD45RA and antiCD45RO or anti-CD29 monoclonal antibodies is also common on CD8+ cells (Clement, 1992). Analyses of more precisely defined lymphocyte subpopulations using these monoclonal antibodies as well as measurement of the cytotoxic T lymphocyte activity would be useful to define them. In addition, it is important to control confounding factors because aging and smoking influence memory T cells (Falcao and De-Santis, 1991; Chavance et al., 1993). In conclusion, it is suggested that CD45RO+ memory T cells may be susceptible to the effects of lead on T cell subpopulations. Further studies are needed to define their functional role. ACKNOWLEDGMENTS We thank Dr. K. Murata for his valuable comment and Dr. S. Suzuki and Dr. H. Wada for their technical assistance.
REFERENCES Chavance, M., Perrot, J. Y., and Annesi, I. (1993). Smoking, CD45RO+ (memory), and CD45RA+ (naive) CD4+ T cells. Am. Rev. Respir. Dis. 148, 237–240. Clement, L. T. (1992). Isoforms of the CD45 common leukocyte antigen family: Markers for human T-cell differentiation. J. Clin. Immunol. 12, 1–10. Cohen, N., Modai, D., Golik, A., Weissgarten, J., Peller, S., Katz, A., Averbukh, Z., and Shaked, U. (1989). Increased concanavalin A-induced suppressor cell activity in humans with occupational lead exposure. Environ. Res. 48, 1–6. Faith, R. E., Luster, M. I., and Kimmel, C. A. (1979). Effect of chronic developmental lead exposure on cell-mediated immune functions. Clin. Exp. Immunol. 35, 413–420. Falcao, R. P., and De-Santis, G. C. (1991). Age-associated changes of memory (CD45RO+) and naive (CD45R+) T cells. Braz. J. Med. Biol. Res. 24, 275–279. Fischbein, A., Tsang, P., Luo, J. J., and Bekesi, J. G. (1993a). The immune system as target for subclinical lead related toxicity. Br. J. Ind. Med. 50, 185–186. Fischbein, A., Tsang, P., Luo, J. J., Roboz, J. P., Jiang, J. D., and Bekesi, J. G. (1993b). Phenotypic aberrations of CD3+ and
64
SATA ET AL.
CD4+ cells and functional impairments of lymphocytes at lowlevel occupational exposure to lead. Clin. Immunol. Immunopathol. 66, 163–168. Landay, A., Gartland, L., and Clement, L. T. (1983). Characterization of a phenotypically distinct subpopulation of Leu-2+ cells which suppresses T cell proliferative responses. J. Immunol. 131, 2757–2761. Mackay, C. R. (1991). T-cell memory: The connection between function, phenotype and migration pathways. Immunol. Today 12, 189–192. McCabe, M. J., Jr., and Lawrence, D. A. (1990). The heavy metal lead exhibits B cell-stimulatory factor activity by enhancing B cell Ia expression and differentiation. J. Immunol. 145, 671– 677. Morimoto, C., Rudd, C. E., Letvin, N. L., and Schlossman, S. F. (1987). A novel epitope of the LFA-1 antigen which can distinguish killer effector and suppressor cells. Nature 330, 479–482. Sanders, M. E., Makgoba, M. W., and Shaw, S. (1988). Human naive and memory T cells: Reinterpretation of helper-inducer and suppressor-inducer subsets. Immunol. Today 9, 195–199.
Sata, F., Araki, S., Sakai, T., Nakata, A., Yamashita, K., Morita, Y., Tanigawa, T., and Miki, A. (1997a). Immunological effects of CaEDTA injection: Observations in two lead workers. Am. J. Ind. Med. 32, 674–680. Sata, F., Araki, S., Tanigawa, T., Morita, Y., Sakurai, S., and Katsuno, N. (1997b). Changes in natural killer cell subpopulations in lead workers. Int. Arch. Occup. Environ. Health 69, 306–310. Sung, H. L., Araki, S., Tanigawa, T., and Sakurai, S. (1995). Selective decrease of the suppressor-inducer (CD4+CD45RA+) T lymphocytes in workers exposed to benzidine and betanaphthylamine. Arch. Environ. Health 50, 196–199. Svenningsson, A., Anderson, O., Hansson, G. K., and Stemme, S. (1995). Reduced frequency of memory CD8+ T lymphocytes in cerebrospinal fluid and blood of patients with multiple sclerosis. Autoimmunity 21, 231–239. Watanabe, T., Fujita, H., Koizumi, A., Chiba, K., Miyasaka, M., and Ikeda, M. (1985). Baseline level of blood lead concentration among Japanese farmers. Arch. Environ. Health 40, 170–176.
76, 61–64 (1998)
ER973790
Changes in T Cell Subpopulations in Lead Workers1 Fumihiro Sata,*,2 Shunichi Araki,* Takeshi Tanigawa,*,3 Yoko Morita,*,4 Susumu Sakurai,† Akinori Nakata,*,4 and Naochika Katsuno* *Department of Public Health, Faculty of Medicine, University of Tokyo, and †Clinical Laboratory, University of Tokyo Hospital, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan Received October 14, 1996
impairments of lymphocytes have been observed (Cohen et al., 1989; Fischbein et al., 1993a,b; Sata et al., 1997a,b). Antigen receptors on the surface of T lymphocytes are associated with small integral membrane proteins called CD3 complexes. Utilizing anti-CD4 and anti-CD8 monoclonal antibodies, it has been possible to divide T lymphocytes into CD4+ helper/ inducer and CD8+ suppressor/cytotoxic cells. From a differential point of view, CD3+ cells and CD4+ cells can be divided into two subpopulations, using antiCD45RA and anti-CD45RO or anti-CD29 monoclonal antibodies (Sanders et al., 1988; Clement, 1992). The subpopulations of CD4+ cells using those monoclonal antibodies had been called ‘‘suppressorinducer’’ and ‘‘helper-inducer’’ T cells because of their functional aspect. However, it is now generally believed that such a subdivision of CD4+ cells is associated with a differentiation stage rather than a functional subset (Sanders et al., 1988).
To investigate the effects of lead on the human immune system, we analyzed T cell subpopulations and B (CD19+) cells in peripheral blood in 71 male lead workers. They were engaged in manufacturing lead stearate in a chemical factory, aged 20 to 74 (mean 48) years. Their blood lead concentrations (PbB) were between 7 and 50 (mean 19) mg/dl. The control group consisted of 28 ‘‘healthy’’ male volunteers without a history of occupational exposure to lead or other hazardous substances, aged 33 to 67 (mean 55) years. In comparison with the controls, a significant reduction in the number of CD3+CD45RO+ (memory T) cells and a significant expansion in the percentage of CD8+ cells in the lead workers were found. There was a significant positive correlation between the percentage of CD3+CD45RA+ (naive T) cells and PbB in the lead workers. It is suggested that CD45RO+ memory T cells may be most susceptible to the effects of lead on T cell subpopulations. © 1998 Academic Press Key Words: lymphocyte subpopulations; lead; memory T cells; CD45RO antigen; T cell differentiation.
MATERIALS AND METHODS
Subjects The 71 male subjects were lead workers engaged in manufacturing lead stearate in a chemical factory. The control group consisted of 28 ‘‘healthy’’ male volunteers working at another chemical factory as security service or clerical works without a history of occupational exposure to lead or other hazardous substances. The demographics of the lead workers and the controls are shown in Table 1. The lead workers’ blood lead concentrations (PbB) were between 7 and 50 (mean 19) mg/dl, whereas their past PbB had been higher as a whole. Currently, a limit of 10 mg/dl (4.9 mg/dl) is considered the upper limit for healthy Japanese men (Watanabe et al., 1985). No subject had signs and symptoms indicative of infection at the time of the study; none had used drugs that could affect immunological analysis.
INTRODUCTION
It has been reported that lead influences the immune system both in animal models and in human subjects. In lead workers, phenotypic aberrations of T cells and natural killer (NK) cells and functional 1 This study was partly supported by Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture in Japan and conducted with all the subjects’ informed consent. 2 To whom correspondence should be addressed: National Cancer Institute, National Institutes of Health, Building 37, Room 3E24, Bethesda, MD 20892. Fax: +1-301-496-8419. 3 Present address: Institute of Community Medicine, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305, Japan. 4 Present address: National Institute of Industrial Health, 621-1 Nagao, Tama-ku, Kawasaki, Kanagawa 214, Japan.
61 0013-9351/98 $25.00 Copyright © 1998 by Academic Press All rights of reproduction in any form reserved.
62
SATA ET AL.
TABLE 1 Demographic Characteristics of 71 Male Lead Workers and 28 Healthy Controlsa Characteristic Age 20–29 30–39 40–49 50–59 ù60 Current smokers ø20 cigarettes/day >20 cigarettes/day Current nonsmokers Exsmokers Never-smokers Blood lead concentration (mg/dl) <10 10–20 20–30 ù30 a b
Lead workers
Controls
5 (7) 13 (18) 19 (27) 25 (35) 9 (13) 42 (59) 28 (39) 14 (20) 29 (41) 21 (30) 8 (11)
0 2 (7) 2 (7) 17 (61) 7 (25) 9 (32) 5 (18) 4 (14) 19 (68) 9 (32) 10 (36)
6 (8) 36 (51) 22 (31) 7 (10)
—b — — —
Number and percentage in parentheses. Not measured.
The procedure was fully explained to all the subjects and this study was conducted with their informed consent. Collection of Blood Samples and Analysis Peripheral blood samples were taken from each individual by venipuncture using ethylenediaminetetraacetic acid (K2-EDTA) as an anticoagulant for measurement of leukocyte count and for immunofluorescence staining and heparin for measurement of PbB. Immunological analysis was conducted within 10 h after the blood samples were collected. All samples were transported and handled at room temperature (15–20°C). The lymphocyte subpopulations were measured using the following pairs of monoclonal antibodies: anti-Leu4 (CD3)/anti-Leu12 (CD19), anti-Leu4/antiLeu45RO (CD45RO), anti-Leu18 (CD45RA, equivalent to 2H4)/anti-Leu4, anti-Leu3 (CD4)/anti-Leu2 (CD8), anti-4B4 (CD29)/anti-Leu3, anti-Leu18/antiLeu3, and mouse IgG1/mouse IgG2a as a negative control (Sata et al., 1997b; Sung et al., 1995). PbB levels were measured by polarized Zeeman atomic absorption spectrophotometry (Z-8100, Hitachi, Tokyo) after 10-fold dilution with 1% ammonium phosphate and 1% Triton X solution. Statistical Methods Differences in age and smoking (numbers of cigarettes smoked per day) between the lead workers
and the controls were statistically significant (P < 0.01 and P < 0.05, respectively; independent t test). Differences in numbers (per mm3 whole blood) and percentages of each lymphocyte subpopulation between the lead workers and the controls were analyzed by analysis of covariance with age and smoking as covariates. The associations between the numbers or percentages of lymphocyte subpopulations and PbB in the lead workers were analyzed by Pearson’s correlation coefficient. Multiple regression analysis was used to identify the model of variables such as exposure of lead (1 in the lead workers and 0 in the controls), smoking, and age which most predicted each lymphocyte subpopulation. All analyses were conducted using SPSS software for Macintosh (SPSS Inc., Chicago, IL). RESULTS
The numbers and percentages of T cell subpopulations and B (CD19+) cells in the lead workers and the controls are shown in Table 2. In comparison with the controls, a significant reduction in the number of CD3+CD45RO+ cells and a significant TABLE 2 Numbers (per mm3 Whole Blood) and Percentages of Lymphocyte Subpopulations in 71 Lead Workers and in 28 Healthy Controlsa Lymphocytes CD3+ cells Number Percentage CD3+CD45RO+ cells Number Percentage CD3+CD45RA+ cells Number Percentage CD4+ cells Number Percentage CD4+CD29+ cells Number Percentage CD4+CD45RA+ cells Number Percentage CD8+ cells Number Percentage CD4/CD8 CD19+ cells Number Percentage
Lead workers
Controls
1570 (570) 60 (11)
1550 (440) 59 (10)
740 (310)* 29 (10)
850 (450) 32 (11)
800 (420) 31 (12)
790 (360) 30 (13)
910 (430) 34 (10)
840 (290) 32 (8)
570 (260) 22 (8)
550 (250) 20 (6)
390 (320) 14 (8)
400 (210) 16 (8)
970 (350) 38 (9)* 1.0 (0.8)
890 (270) 34 (7) 1.0 (0.4)
300 (210) 11 (6)
320 (190) 12 (5)
a Mean and standard deviation in parentheses. * P < 0.05 (analysis of covariance with age and smoking as covariates, compared with the controls).
63
T CELL SUBPOPULATIONS IN LEAD WORKERS
expansion in the percentage of CD8+ cells in the lead workers were found. There was a significant positive correlation between the percentage of CD3+CD45RA+ cells and PbB in the lead workers (P < 0.05). In multiple regression analysis, there was also a significant relationship between the number of CD3+CD45RO+ cells and exposure to lead; regression coefficient (B) and standard error (SE) are −172.4 (P < 0.05) and 79.4, respectively. DISCUSSION
In the present study, we have shown a selective decrease in the number of CD3+CD45RO+ cells in peripheral blood in the lead workers compared with the controls. We have also found that there was a dose-related increase in the percentage of CD3+CD45RA+ cells in the lead workers. Those changes seemed to be associated with each other. Among the membrane antigens that are differentially expressed by reciprocal human T cell subpopulations are the CD45RA and CD45RO isoforms of the common leukocyte antigen family, which have been hypothesized to identify ‘‘naive’’ and ‘‘memory’’ T cells, respectively (Clement, 1992). Memory T cells differ from naive T cells in that they have been activated (typically by antigen) at some time after export from thymus (Sanders et al., 1988). On the other hand, it has been suggested that the adverse effect of lead might be due to its high affinity for the T cell receptor (TCR) interfering with antigen processing from monocytes to T lymphocytes (Fischbein et al., 1993b). There is a possibility that lead may inhibit T cells from being activated or coexpressing CD45RO antigen in T cell differentiation or maturation on account of its high affinity for TCR. Memory T cells preferentially migrate through peripheral organs such as the skin, whereas naive T cells migrate through organized lymphoid organs such as lymph nodes (Mackay, 1991). It has been suggested that normal homing patterns of lymphocytes might be altered by exposure to lead (Faith et al., 1979). There is another possibility that lead may allow CD45RO+ T cells to migrate through peripheral organs more preferentially. We could not detect any significant changes in the numbers and percentages of CD4+ cells and their subpopulations in the lead workers. However, those observations suggested that a reduction in memory T cells in the lead workers might occur mainly in memory CD8+ cells. Similar observations were found in patients with multiple sclerosis and such changes could indicate a defective differentiation into mature CD8+ cells (Svenningsson et al., 1995).
A possibility that lead might be associated with autoimmune diseases has been proposed (McCabe and Lawrence, 1990). However, the association between exposure to lead and autoimmunity remains unclear. On the other hand, increased concanavalin Ainduced suppressor cell activity in lead workers has been reported (Cohen et al., 1989). Further studies are needed to define whether CD8+CD45RO+ cells decrease actually and whether such a decrease, if it occurs, represents a decrease of cells with primarily suppressor or cytotoxic functions. It has been possible to subdivide CD8+ cells functionally into the suppressor cells and the cytotoxic effector cells, utilizing anti-CD11b and anti-CD11a monoclonal antibodies (Landay et al., 1983; Morimoto et al., 1987). Recently, subdivision with anti-CD45RA and antiCD45RO or anti-CD29 monoclonal antibodies is also common on CD8+ cells (Clement, 1992). Analyses of more precisely defined lymphocyte subpopulations using these monoclonal antibodies as well as measurement of the cytotoxic T lymphocyte activity would be useful to define them. In addition, it is important to control confounding factors because aging and smoking influence memory T cells (Falcao and De-Santis, 1991; Chavance et al., 1993). In conclusion, it is suggested that CD45RO+ memory T cells may be susceptible to the effects of lead on T cell subpopulations. Further studies are needed to define their functional role. ACKNOWLEDGMENTS We thank Dr. K. Murata for his valuable comment and Dr. S. Suzuki and Dr. H. Wada for their technical assistance.
REFERENCES Chavance, M., Perrot, J. Y., and Annesi, I. (1993). Smoking, CD45RO+ (memory), and CD45RA+ (naive) CD4+ T cells. Am. Rev. Respir. Dis. 148, 237–240. Clement, L. T. (1992). Isoforms of the CD45 common leukocyte antigen family: Markers for human T-cell differentiation. J. Clin. Immunol. 12, 1–10. Cohen, N., Modai, D., Golik, A., Weissgarten, J., Peller, S., Katz, A., Averbukh, Z., and Shaked, U. (1989). Increased concanavalin A-induced suppressor cell activity in humans with occupational lead exposure. Environ. Res. 48, 1–6. Faith, R. E., Luster, M. I., and Kimmel, C. A. (1979). Effect of chronic developmental lead exposure on cell-mediated immune functions. Clin. Exp. Immunol. 35, 413–420. Falcao, R. P., and De-Santis, G. C. (1991). Age-associated changes of memory (CD45RO+) and naive (CD45R+) T cells. Braz. J. Med. Biol. Res. 24, 275–279. Fischbein, A., Tsang, P., Luo, J. J., and Bekesi, J. G. (1993a). The immune system as target for subclinical lead related toxicity. Br. J. Ind. Med. 50, 185–186. Fischbein, A., Tsang, P., Luo, J. J., Roboz, J. P., Jiang, J. D., and Bekesi, J. G. (1993b). Phenotypic aberrations of CD3+ and
64
SATA ET AL.
CD4+ cells and functional impairments of lymphocytes at lowlevel occupational exposure to lead. Clin. Immunol. Immunopathol. 66, 163–168. Landay, A., Gartland, L., and Clement, L. T. (1983). Characterization of a phenotypically distinct subpopulation of Leu-2+ cells which suppresses T cell proliferative responses. J. Immunol. 131, 2757–2761. Mackay, C. R. (1991). T-cell memory: The connection between function, phenotype and migration pathways. Immunol. Today 12, 189–192. McCabe, M. J., Jr., and Lawrence, D. A. (1990). The heavy metal lead exhibits B cell-stimulatory factor activity by enhancing B cell Ia expression and differentiation. J. Immunol. 145, 671– 677. Morimoto, C., Rudd, C. E., Letvin, N. L., and Schlossman, S. F. (1987). A novel epitope of the LFA-1 antigen which can distinguish killer effector and suppressor cells. Nature 330, 479–482. Sanders, M. E., Makgoba, M. W., and Shaw, S. (1988). Human naive and memory T cells: Reinterpretation of helper-inducer and suppressor-inducer subsets. Immunol. Today 9, 195–199.
Sata, F., Araki, S., Sakai, T., Nakata, A., Yamashita, K., Morita, Y., Tanigawa, T., and Miki, A. (1997a). Immunological effects of CaEDTA injection: Observations in two lead workers. Am. J. Ind. Med. 32, 674–680. Sata, F., Araki, S., Tanigawa, T., Morita, Y., Sakurai, S., and Katsuno, N. (1997b). Changes in natural killer cell subpopulations in lead workers. Int. Arch. Occup. Environ. Health 69, 306–310. Sung, H. L., Araki, S., Tanigawa, T., and Sakurai, S. (1995). Selective decrease of the suppressor-inducer (CD4+CD45RA+) T lymphocytes in workers exposed to benzidine and betanaphthylamine. Arch. Environ. Health 50, 196–199. Svenningsson, A., Anderson, O., Hansson, G. K., and Stemme, S. (1995). Reduced frequency of memory CD8+ T lymphocytes in cerebrospinal fluid and blood of patients with multiple sclerosis. Autoimmunity 21, 231–239. Watanabe, T., Fujita, H., Koizumi, A., Chiba, K., Miyasaka, M., and Ikeda, M. (1985). Baseline level of blood lead concentration among Japanese farmers. Arch. Environ. Health 40, 170–176.