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Changes in macrophages in vivo induced by desensitization
CELLULAR
IMMUNOLOGY
23,171-176
(1976)
SHORT COMMUNICATION Changes in Macrophages in Vivo Induced by Desensitization L. W. Department
of Pathology,
Royal
POULTER
J. L.
l AND
TURK
College of Surgeons of England, Lo+tdon WCZA 3PN, England Receizped Jarmary
35-43 Lilzcoln’s
Inn Fields,
8, 1976
Peritoneal exudate macrophages were removed from animals sensitized to horse cytochrome c and from similar animals which had been desensitized with this antigen. The ability of lymphokine to induce migration inhibition and also alterations of the level of glucose oxidation in these cells has been examined. It was found that for a transient period after the desensitization, macrophages removed from the peritoneum were unresponsive to lymphokine in the migration inhibition assay. At the same time, culturing these cells with lymphokine for 1 hr caused a significant rise in their glucose oxidation activity. It is suggested from these results that desensitization may result in macrophage activation in z&o. This is discussed in relation to current concepts of the mechanisms of desensitization.
INTRODUCTION When sensitized guinea pigs are subsequently given a large dose of the sensitizing antigen their ability to mount a delayed hypersensitivity (DH) reaction to that antigen is lost (l-3). This loss is transient and is accompanied by a loss of responsiveness in the in vitro assays of cell mediated immunity (CMI) (4-6). This phenomenon has been described as desensitization, and it is further characterised by the fact that the loss of responsiveness is initially non-specific, that is, the DH response to other antigens, (to which the animal has also been sensitized), is also suppressed ( 1,7,S). It has been variously suggested that desensitization is a result of a compartmentalisation of reactive lymphocytes into lymph nodes (4)) the stimulation of suppressor cells to liberate blocking factors (7, 8) ; or the production of specific antibody which blocks the CM1 response (9). No attempt has so far been made to look at the macrophages of the desensitized animals. As these cells are intimately involved both in DH reactions and in the in z&vu assays of CM1 it seems important to examine their status following desensitization. Previous work (10, ll), has demonstrated that lymphokine has a biphasic effect on macrophages in vitro. An early physiological effect which results in migration inhibition is succeeded by activation of the cells as determined by spreading and 1 Present address for correspondence: York
Trudeau
12983. 171
Copyright 1976 by Academic Press. Inc. All rights oQ reproduction in any form resewed.
Inst. Inc., P. 0. Box 59, Saranac
Lake,
New
172
SHORT
COMMUNICATION
vacuolation of the cytoplasm and increased glucose oxidation. It would appear from these results that migration inhibition and activation could not occur at the same time. Because of this it seemed possible that changes in macrophage status in V&JO might be detectable by examining the response of these cells to subsequent lymphokine contact in vitro. MATERIALS
AND METHODS
Aninzals. Female Hartley strain guinea pigs weighing 400-500 g were used throughout. When necessary these were killed by ether anaesthesia. Lymphokine. Lymphokine and corresponding control fractions were prepared as described previously (10) in a separate system using bovine gamma globulin as the inducing antigen. These were partially purified on Sephadex GlOO to a molecular weight range 25-75 x 103, concentrated at 12.5 x the original supernatant concentrations and stored freeze-dried until used. Sensitization and desensitization. Animals were sensitized with 1 mg of horse cytochrome c (cyto. c.) as described previously (12). Fourteen days after sensitization some animals were injected i/v with 500 ,ug of cyto. c dissolved in 0.1 ml of sterile saline. Skin testing. Skin tests were performed by injecting 100 pg cyto. c., (dissolved in 0.1 ml sterile saline), i/d in the shaved flank. Reactions were quantitated by measuring the increase in skin thickness at the injection site with a skin micrometer. Peritoneal exudates. Peritoneal exudates were stimulated with sterile liquid paraffin. This was injected into the peritoneum 4 days before the cells were to be harvested. Migration inhibition. Macrophage migration was performed by the method of David et al. (13). The migration areas were projected and measured with a planimeter. In some experiments migration inhibition in the presence ‘of cyto. c., (100 pg/ml), was examined and percentage inhibition was calculated by the formula, 100 -
migration area with antigen x 100 migration area without antigen >
In other experiments migration inhibition in the presence of lymphokine examined and the percentage inhibition was calculated by the formula, migration area with lymphokine 100 - migration area with control fraction
x 100
was
>
Glucose oxidation. Macrophage monolayers were prepared as described previously (10). The PECs were plated onto coverslips in Leighton tubes and cultured for 1 hr in Eagles medium containing 15% foetal calf serum. They were then vigorously washed with fresh medium to remove non-adherent cells and cultured for a further hour in Eagles medium containing 50% normal guinea pig serum. Either lymphokine or control fractions were added to this medium at an equivalent concentration to that used for the migration inhibition experiments. After this hour of culture glucose6phosphate dehydrogenase activity was measured in the cehs as a marker for glucose oxidation, using a cytochemical method previously described in full (10).
SHORT
TABLE Animal
status
Sensitized to cyto. c. 15 days previously As above but desensitized 24 hr before the tests 7 days after the desensitizing injection Normal
173
COMMUNICATION
1
24 hr DH reaction”
y0 Migration inhibition (by cyto. c.)
0.56 h 0.15 mmb
42.72 f
3c
0.28 f
0.07 mm
19.17 f
6.2
0.58 f
0.12 mm
39.4 zt 6.2 9.12 % 2.3
a Animals challenged with 100 pg cyto. c. i/d in the flank. b Mean increase in skin thickness f standard error, (groups of five animals in each case). c Mean migration inhibition & standard error from groups of five animals in each case. Quadruplicate capillaries were set up from each individual animal.
RESULTS Desensitization. Animals sensitized to cyto. c. 15 days previously demonstrated DH to this antigen if challenged intradermally and PECs from these animals were inhibited from migrating by cyto. c. in vitro, (Table 1). The intravenous injection of cyto. c. into these animals however, caused a marked reduction in skin test reactivity and migration inhibition responsiveness. This loss of reactivity was only transient and by 7 days normal responsiveness in both these assay systems had returned. Migration inhibition by lyvnphokine. The PECs from sensitized and desensitized animals were allowed to migrate in the presence of lymphokine at a concentration known to inhibit the migration of normal cells by approximately 50%. In Fig. 1 it can be seen ,that macrophages harvested from animals 1 and 3 days after the desensitizing injection failed to be inhibited by this lymphokine. Cells taken 7 days
FIG. 1. The percentage inhibition of migration induced by lymphokine on peritoneal exudate cells taken at various times after desensitization. The value at time zero represents the level of migration inhibition of cells taken from sensitized but not desensitized animals. Point N represents the level of migration inhibition of peritoneal exudate cells from normal animals.
174
SHORT
COMMUNICATION
TABLE
2
The Effect of 1 hr Culture with Lymphokine or Control Fraction* Oxidation of Macrophages from Sensitized and Desensitized Animal
status
Experiment
on the Glucose Animals
Glucose oxidation after contact with Control fraction
Sensitized
to cyto. c.
Lymphokine
1 2
359.0 443.5
i 14.1a zk 37.8
1
293.0 402.8 333.0 130.0 263.25
f zk III i +
33 31 56 20 13.3
307.1 525.5 411.5 208.27
It zt f zk
35.9 50.8 59 31
303.17 397.68 268.68 219.14
=t f f dz
34.2 34 31 18.2
P > 24 hr after desensitization
2 3 4 5
P < 3 days after desensitization
1
2 3 4
349.9 440.4
h 50.8 zk 7.4
0.16
295.0 543.9 403.0 186.0 372.0
j, f * f zt
26 49 37 29 30
f zt zk f
44 81 49 35.4
f f f f
35.3 36.9 46.4 23
0.01
520.29 536.1 889.0 662.13
P < 0.05 7 days after desensitization
1 2 3 4
518.36 349.9 178.13 171.0
P > 0.1 * Identical Sephadex fraction to the lymphokine but prepared from sensitized lymph node cell cultures without the addition of antigen. The antigen was added after culture but before subsequent purification and fractionation. Qnmols hydrogen liberated by lo6 cells in 10 min. Mean & standard error of quadruplicate cultures. b Student’s t test for paired data.
after desensitization had recovered the ability to respond to an equivalent extent to that of cells from sensitized animals not given the desensitizing injection. This level was however lower than the degree of migration inhibition seen when normal cells were used. The normal migration of cells taken from all groups of animals did not differ significantly and although there was a reduction in the number of cells in the exudates from the desensitized animals the proportion of macrophages remained above 60%. Glucose oxidation. In concurrent experiments to the above, peritoneal macrophages were cultured on coverslips, and the level of glucosed-phosphate dehydrogenase activity was measured in these cells after 1 hr contact with lymphokine. The results are shown in Table 2. Twenty-four hours after the desensitizing injection, (in four out of five experiments), those cells that were unresponsive in the migration inhibition assay, responded to lymphokine contact in culture with significant increases in glucose oxidaton. Three days after desensitization similar results were found in three out of four experiments. However, no significant change in activity after lymphokine treatment was found in the cells from animals that had not been desensitized ‘or those taken 7 days after the desensitizing injection.
SHORT
COMMUNICATION
175
DISCUSSION One of the results of desensitization is a loss of responsiveness in the in vitro correlates of DH (4-6). As macrophages are intimately involved in these assays it seemed relevant to examine any change in the status of these cells following desensitization. Macrophage migration inhibition by specific antigen requires that the lymphocytes present in the peritoneal exudates release lymphokines and that the macrophages respond to this. Lack of responsiveness could therefore result from changes in the lymphocyte or macrophage populations. In the present work it has been demonstrated that the macrophages from desensitized animals cannot be inhibited from migrating even when lymphokine prepared eleswhere is added to them. This would indicate that some direct effect on the macrophage has resulted from the desensitization. Increased glucose oxidation has been taken as a characteristic of macrophages activated by prolonged contact, (48-72 hr), with lymphokine in vitro (11, 14). The results above therefore suggest that the cells removed 1 and 3 days after desensitization had been at least partially activated in v&o before removal. This suggestion is supported by the observation that these cells could not be inhibited from migrating by lymphokine, since this functional response seems to occur prior to activation of the cells (15). Although no antibody has as yet been detected in the serum of guinea pigs sensitized with cyto. c. (12) it cannot be excluded that the change in macrophage status might have resulted from immune complex activation in viva. A further explanation for the loss ,of responsiveness might be the compartmentalisation of sensitized lymphocytes. This, however, would not explain why the macrophages showed increased glucose oxidation rapidly after lymphokine contact, nor why they could not be inhibited from migrating by lymphokine. These results indicate, that following desensitization activation of macrophages occurs in vtio. This activation may then render the macrophages unable to express migration inhibition on subsequent contact with lymphokine in vitro, and might prevent their attraction and retention at a skin test site when the animal is challenged intradermally. That this activation occurs following lymphokine release in viva remains an assumption but it might explain the need for antigen to react with sensitized but not tolerant cells to create a state of desensitization (8)) and the increased proliferation of lymph node cells in viva, also seen following a desensitizing injection (15). This hypothesis is not consistent with the observations of Liew (9) which clearly indicate some type of “enhancing” antibody as being responsible for the loss of reactivity; however he was using both a different animal species and different antigen. It is also difficult to explain why lymphokine, (skin reactive factor, SRF), will produce an inflammatory reaction when injected intradermally into a desensitized animal (7). It has been suggested however, that the involvement of macrophages in DH reactions to specific antigens is different from their involvement in the SRF reaction (16). The suggestion that desensitization affects the effector arm of the immune response by altering macrophage status, is consistent with the observations that the effect is initially non-specific ( 1, 7, 8) and that lymph node cells from desensitized animals can still passively transfer sensitivity to a normal animal (7, 8). In any case, the ability to desensitize animals with an antigen that produces no detectable antibody #responsewarrants further examination.
176
SHORT
COMMUNICATION
REFERENCES 1. Uhr. J. W., and Pappenheimer, A. M., J. Exp. Med. 108, 891, 1958. 2. Schlossman, S. F., and Levine, H., J. Immunol. 99, 111, 1967. 3. Asherson, G. L., and Stone, S. H., Immunology 13, 469, 1967. 4. Schlossman, S. F., Levin. H. A., Rocklin, R. E., and David, J. R. J. Exp. Med. 134, 741, 1971. 5. Jokipii, L., Immunology, 25, 283, 1973. 6. Jokipii, L., and Kosunen, T. U., Cell. Zmmunol. 10, 196, 1974. 7. Dwyer, J. M., and Kantor, F. S., J. Exp. Med. 137, 32, 1973. 8. Dwyer, J. M., and Kantor, F. S., J. Exg. Med. 142, 588, 1975. 9. Liew, F. Y., Cell. Immzllzol. 19, 129, 1975. 10. Poulter, L. W., and Turk, J. L., Cell. Immunol. 20, 12, 1975. 11. Poulter. L. W., and Turk, J. L., Cell. Immunol. 20, 25, 1975 12. Reichlin, M., and Turk, J. L., Nature 251, 355, 1974. 13. David. J. R., Al. Askaris, S., Lawrence, H. S., and Thomas, L., J. Zmmunol. 93, 264, 1964. 14. Nathan, C. F., Remold, H. G., and David, J. R., J. Exp. Med. 137, 275, 1973. 15. Nath, Indira, Poulter, L. W., and Turk, J. L., Clin. exp. Immunol. 13, 275, 1973. 16. Phanuphak, P., Moorhead, J. W.. and Claman, H. N., J. Immunol. 114, 1147, 1975. 17. Schwartz, H. J., and Catanzaro, P. J., Int. Arch. Allergy, Appl. Immunol. 44, 409, 1973.
IMMUNOLOGY
23,171-176
(1976)
SHORT COMMUNICATION Changes in Macrophages in Vivo Induced by Desensitization L. W. Department
of Pathology,
Royal
POULTER
J. L.
l AND
TURK
College of Surgeons of England, Lo+tdon WCZA 3PN, England Receizped Jarmary
35-43 Lilzcoln’s
Inn Fields,
8, 1976
Peritoneal exudate macrophages were removed from animals sensitized to horse cytochrome c and from similar animals which had been desensitized with this antigen. The ability of lymphokine to induce migration inhibition and also alterations of the level of glucose oxidation in these cells has been examined. It was found that for a transient period after the desensitization, macrophages removed from the peritoneum were unresponsive to lymphokine in the migration inhibition assay. At the same time, culturing these cells with lymphokine for 1 hr caused a significant rise in their glucose oxidation activity. It is suggested from these results that desensitization may result in macrophage activation in z&o. This is discussed in relation to current concepts of the mechanisms of desensitization.
INTRODUCTION When sensitized guinea pigs are subsequently given a large dose of the sensitizing antigen their ability to mount a delayed hypersensitivity (DH) reaction to that antigen is lost (l-3). This loss is transient and is accompanied by a loss of responsiveness in the in vitro assays of cell mediated immunity (CMI) (4-6). This phenomenon has been described as desensitization, and it is further characterised by the fact that the loss of responsiveness is initially non-specific, that is, the DH response to other antigens, (to which the animal has also been sensitized), is also suppressed ( 1,7,S). It has been variously suggested that desensitization is a result of a compartmentalisation of reactive lymphocytes into lymph nodes (4)) the stimulation of suppressor cells to liberate blocking factors (7, 8) ; or the production of specific antibody which blocks the CM1 response (9). No attempt has so far been made to look at the macrophages of the desensitized animals. As these cells are intimately involved both in DH reactions and in the in z&vu assays of CM1 it seems important to examine their status following desensitization. Previous work (10, ll), has demonstrated that lymphokine has a biphasic effect on macrophages in vitro. An early physiological effect which results in migration inhibition is succeeded by activation of the cells as determined by spreading and 1 Present address for correspondence: York
Trudeau
12983. 171
Copyright 1976 by Academic Press. Inc. All rights oQ reproduction in any form resewed.
Inst. Inc., P. 0. Box 59, Saranac
Lake,
New
172
SHORT
COMMUNICATION
vacuolation of the cytoplasm and increased glucose oxidation. It would appear from these results that migration inhibition and activation could not occur at the same time. Because of this it seemed possible that changes in macrophage status in V&JO might be detectable by examining the response of these cells to subsequent lymphokine contact in vitro. MATERIALS
AND METHODS
Aninzals. Female Hartley strain guinea pigs weighing 400-500 g were used throughout. When necessary these were killed by ether anaesthesia. Lymphokine. Lymphokine and corresponding control fractions were prepared as described previously (10) in a separate system using bovine gamma globulin as the inducing antigen. These were partially purified on Sephadex GlOO to a molecular weight range 25-75 x 103, concentrated at 12.5 x the original supernatant concentrations and stored freeze-dried until used. Sensitization and desensitization. Animals were sensitized with 1 mg of horse cytochrome c (cyto. c.) as described previously (12). Fourteen days after sensitization some animals were injected i/v with 500 ,ug of cyto. c dissolved in 0.1 ml of sterile saline. Skin testing. Skin tests were performed by injecting 100 pg cyto. c., (dissolved in 0.1 ml sterile saline), i/d in the shaved flank. Reactions were quantitated by measuring the increase in skin thickness at the injection site with a skin micrometer. Peritoneal exudates. Peritoneal exudates were stimulated with sterile liquid paraffin. This was injected into the peritoneum 4 days before the cells were to be harvested. Migration inhibition. Macrophage migration was performed by the method of David et al. (13). The migration areas were projected and measured with a planimeter. In some experiments migration inhibition in the presence ‘of cyto. c., (100 pg/ml), was examined and percentage inhibition was calculated by the formula, 100 -
migration area with antigen x 100 migration area without antigen >
In other experiments migration inhibition in the presence of lymphokine examined and the percentage inhibition was calculated by the formula, migration area with lymphokine 100 - migration area with control fraction
x 100
was
>
Glucose oxidation. Macrophage monolayers were prepared as described previously (10). The PECs were plated onto coverslips in Leighton tubes and cultured for 1 hr in Eagles medium containing 15% foetal calf serum. They were then vigorously washed with fresh medium to remove non-adherent cells and cultured for a further hour in Eagles medium containing 50% normal guinea pig serum. Either lymphokine or control fractions were added to this medium at an equivalent concentration to that used for the migration inhibition experiments. After this hour of culture glucose6phosphate dehydrogenase activity was measured in the cehs as a marker for glucose oxidation, using a cytochemical method previously described in full (10).
SHORT
TABLE Animal
status
Sensitized to cyto. c. 15 days previously As above but desensitized 24 hr before the tests 7 days after the desensitizing injection Normal
173
COMMUNICATION
1
24 hr DH reaction”
y0 Migration inhibition (by cyto. c.)
0.56 h 0.15 mmb
42.72 f
3c
0.28 f
0.07 mm
19.17 f
6.2
0.58 f
0.12 mm
39.4 zt 6.2 9.12 % 2.3
a Animals challenged with 100 pg cyto. c. i/d in the flank. b Mean increase in skin thickness f standard error, (groups of five animals in each case). c Mean migration inhibition & standard error from groups of five animals in each case. Quadruplicate capillaries were set up from each individual animal.
RESULTS Desensitization. Animals sensitized to cyto. c. 15 days previously demonstrated DH to this antigen if challenged intradermally and PECs from these animals were inhibited from migrating by cyto. c. in vitro, (Table 1). The intravenous injection of cyto. c. into these animals however, caused a marked reduction in skin test reactivity and migration inhibition responsiveness. This loss of reactivity was only transient and by 7 days normal responsiveness in both these assay systems had returned. Migration inhibition by lyvnphokine. The PECs from sensitized and desensitized animals were allowed to migrate in the presence of lymphokine at a concentration known to inhibit the migration of normal cells by approximately 50%. In Fig. 1 it can be seen ,that macrophages harvested from animals 1 and 3 days after the desensitizing injection failed to be inhibited by this lymphokine. Cells taken 7 days
FIG. 1. The percentage inhibition of migration induced by lymphokine on peritoneal exudate cells taken at various times after desensitization. The value at time zero represents the level of migration inhibition of cells taken from sensitized but not desensitized animals. Point N represents the level of migration inhibition of peritoneal exudate cells from normal animals.
174
SHORT
COMMUNICATION
TABLE
2
The Effect of 1 hr Culture with Lymphokine or Control Fraction* Oxidation of Macrophages from Sensitized and Desensitized Animal
status
Experiment
on the Glucose Animals
Glucose oxidation after contact with Control fraction
Sensitized
to cyto. c.
Lymphokine
1 2
359.0 443.5
i 14.1a zk 37.8
1
293.0 402.8 333.0 130.0 263.25
f zk III i +
33 31 56 20 13.3
307.1 525.5 411.5 208.27
It zt f zk
35.9 50.8 59 31
303.17 397.68 268.68 219.14
=t f f dz
34.2 34 31 18.2
P > 24 hr after desensitization
2 3 4 5
P < 3 days after desensitization
1
2 3 4
349.9 440.4
h 50.8 zk 7.4
0.16
295.0 543.9 403.0 186.0 372.0
j, f * f zt
26 49 37 29 30
f zt zk f
44 81 49 35.4
f f f f
35.3 36.9 46.4 23
0.01
520.29 536.1 889.0 662.13
P < 0.05 7 days after desensitization
1 2 3 4
518.36 349.9 178.13 171.0
P > 0.1 * Identical Sephadex fraction to the lymphokine but prepared from sensitized lymph node cell cultures without the addition of antigen. The antigen was added after culture but before subsequent purification and fractionation. Qnmols hydrogen liberated by lo6 cells in 10 min. Mean & standard error of quadruplicate cultures. b Student’s t test for paired data.
after desensitization had recovered the ability to respond to an equivalent extent to that of cells from sensitized animals not given the desensitizing injection. This level was however lower than the degree of migration inhibition seen when normal cells were used. The normal migration of cells taken from all groups of animals did not differ significantly and although there was a reduction in the number of cells in the exudates from the desensitized animals the proportion of macrophages remained above 60%. Glucose oxidation. In concurrent experiments to the above, peritoneal macrophages were cultured on coverslips, and the level of glucosed-phosphate dehydrogenase activity was measured in these cells after 1 hr contact with lymphokine. The results are shown in Table 2. Twenty-four hours after the desensitizing injection, (in four out of five experiments), those cells that were unresponsive in the migration inhibition assay, responded to lymphokine contact in culture with significant increases in glucose oxidaton. Three days after desensitization similar results were found in three out of four experiments. However, no significant change in activity after lymphokine treatment was found in the cells from animals that had not been desensitized ‘or those taken 7 days after the desensitizing injection.
SHORT
COMMUNICATION
175
DISCUSSION One of the results of desensitization is a loss of responsiveness in the in vitro correlates of DH (4-6). As macrophages are intimately involved in these assays it seemed relevant to examine any change in the status of these cells following desensitization. Macrophage migration inhibition by specific antigen requires that the lymphocytes present in the peritoneal exudates release lymphokines and that the macrophages respond to this. Lack of responsiveness could therefore result from changes in the lymphocyte or macrophage populations. In the present work it has been demonstrated that the macrophages from desensitized animals cannot be inhibited from migrating even when lymphokine prepared eleswhere is added to them. This would indicate that some direct effect on the macrophage has resulted from the desensitization. Increased glucose oxidation has been taken as a characteristic of macrophages activated by prolonged contact, (48-72 hr), with lymphokine in vitro (11, 14). The results above therefore suggest that the cells removed 1 and 3 days after desensitization had been at least partially activated in v&o before removal. This suggestion is supported by the observation that these cells could not be inhibited from migrating by lymphokine, since this functional response seems to occur prior to activation of the cells (15). Although no antibody has as yet been detected in the serum of guinea pigs sensitized with cyto. c. (12) it cannot be excluded that the change in macrophage status might have resulted from immune complex activation in viva. A further explanation for the loss ,of responsiveness might be the compartmentalisation of sensitized lymphocytes. This, however, would not explain why the macrophages showed increased glucose oxidation rapidly after lymphokine contact, nor why they could not be inhibited from migrating by lymphokine. These results indicate, that following desensitization activation of macrophages occurs in vtio. This activation may then render the macrophages unable to express migration inhibition on subsequent contact with lymphokine in vitro, and might prevent their attraction and retention at a skin test site when the animal is challenged intradermally. That this activation occurs following lymphokine release in viva remains an assumption but it might explain the need for antigen to react with sensitized but not tolerant cells to create a state of desensitization (8)) and the increased proliferation of lymph node cells in viva, also seen following a desensitizing injection (15). This hypothesis is not consistent with the observations of Liew (9) which clearly indicate some type of “enhancing” antibody as being responsible for the loss of reactivity; however he was using both a different animal species and different antigen. It is also difficult to explain why lymphokine, (skin reactive factor, SRF), will produce an inflammatory reaction when injected intradermally into a desensitized animal (7). It has been suggested however, that the involvement of macrophages in DH reactions to specific antigens is different from their involvement in the SRF reaction (16). The suggestion that desensitization affects the effector arm of the immune response by altering macrophage status, is consistent with the observations that the effect is initially non-specific ( 1, 7, 8) and that lymph node cells from desensitized animals can still passively transfer sensitivity to a normal animal (7, 8). In any case, the ability to desensitize animals with an antigen that produces no detectable antibody #responsewarrants further examination.
176
SHORT
COMMUNICATION
REFERENCES 1. Uhr. J. W., and Pappenheimer, A. M., J. Exp. Med. 108, 891, 1958. 2. Schlossman, S. F., and Levine, H., J. Immunol. 99, 111, 1967. 3. Asherson, G. L., and Stone, S. H., Immunology 13, 469, 1967. 4. Schlossman, S. F., Levin. H. A., Rocklin, R. E., and David, J. R. J. Exp. Med. 134, 741, 1971. 5. Jokipii, L., Immunology, 25, 283, 1973. 6. Jokipii, L., and Kosunen, T. U., Cell. Zmmunol. 10, 196, 1974. 7. Dwyer, J. M., and Kantor, F. S., J. Exp. Med. 137, 32, 1973. 8. Dwyer, J. M., and Kantor, F. S., J. Exg. Med. 142, 588, 1975. 9. Liew, F. Y., Cell. Immzllzol. 19, 129, 1975. 10. Poulter, L. W., and Turk, J. L., Cell. Immunol. 20, 12, 1975. 11. Poulter. L. W., and Turk, J. L., Cell. Immunol. 20, 25, 1975 12. Reichlin, M., and Turk, J. L., Nature 251, 355, 1974. 13. David. J. R., Al. Askaris, S., Lawrence, H. S., and Thomas, L., J. Zmmunol. 93, 264, 1964. 14. Nathan, C. F., Remold, H. G., and David, J. R., J. Exp. Med. 137, 275, 1973. 15. Nath, Indira, Poulter, L. W., and Turk, J. L., Clin. exp. Immunol. 13, 275, 1973. 16. Phanuphak, P., Moorhead, J. W.. and Claman, H. N., J. Immunol. 114, 1147, 1975. 17. Schwartz, H. J., and Catanzaro, P. J., Int. Arch. Allergy, Appl. Immunol. 44, 409, 1973.