Reduced natural killer cell cytotoxicity in depression but not in schizophrenia

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1131

Reduced Natural Killer Cell Cytotoxicity in Depression but Not in Schizophrenia Cindy L. Caldwell, Michael Irwin, and James

A reduction of natural killer (NK) cell activiD, has been found in hospitalized patients with major depressive disorder. To examine whether a reduction of NK activi~' is f o u ~ in other p~,chiatric patients or related to the nonspecific effects of hospitalization. NK cell cytotoxiciQ" was compared in hospitalized depressed patients, schizophrenic inpatients, a.,ut two groups of controls separately age matched to each patient group. NK activi~, was significantly ( p < 0.01) lower in depressed inpatients than control subjects. However. in the hospitalized schizophrenic patients values of natural cytotoxiciry did not differ from controls. These findings suggest that reduced NK cytotoxicity in depression is independent of the effects of hospitalization.

Introduction Clinical studies of immune function in depression have demonstrated that the Iymphocytes of depressed inpatients show a suppressed ability to respond to ~ t o g e n i c stimulation (Kronfol e', a! !983; Schleifer et al 1984; Dt~ko et al 1989), as well as a reduction of natural killer (NK) cytolytic activity as compared with cells obtained from age-matched control subjects (Irwin et al 1987a, 1990a, 1990b; Mohl et al 1987; Kronfol et al 1989; Urch et all 1988). Severity of depressive symptoms, age, and past history of alcohol abuse are all factors that appear to contribute to the immune alterations found in depressed inpatients (Schleifer et al 198~; Irwin e: ~ 1990b). Not all studies have found depression-related alterations in cellular ~ u n e measures such as natural killer (NK) activity, an immune parameter important in host resistance to viral infections (Bukowski et at 1985; Habu et al 1984). For example, neither Schleifer and colleagues (1989) nor Miller et al (1991) found differences in NK activity between depressives and respective controls. However, both of these studies included inpatient and outpatient depressives, and it is possible th?t only inpatient depressives show a reduction in cellular immunity, due either to increased severity of depressive symptoms or the nonspecific effects of hospitalization stress. Even rather modest life stressors such as academic examinations are known to reduce NK activity (Kiecolt-Glaser et al 1984). The purpose of this study is to evaluate whether the effects of hospitalization stress might account for the previously reported reduction of NK activity in depressed inpatients.

From the Departments of Psychiatry, San Diego Veterans Affairs Medical Center and University of California. San Diego, La Jo|la, CA 92093. Address reprint requests to M. Irwin. Department of Psychiatry (V116A), San Diego Veterans Affairs Medical Center, 3350 La Joila Village Drive. San Diego, CA 92161. Received January 28. 1991. revised June 25. 1991. Published !991 by Elsevier Science Publishing Company, Inc.

ISSN/91/$0.00

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C.L. Caldw¢ll et al

BIOL PSYCHIATRY 1991;30:1131-1138

Values of NK activity in two groups of hospitalized psychiatric inpatients, depressives ~ d schizophrenics, were compared with these in two respective groups of a g e - m a t c ~ controls. In addition, because of the still unresolved issue of reduced NK activity, in schizophrenia (Urch et al 1988; Delisi et al 1983; Schindler et al 1986; Kronfol et Ill 1990), measurement of NK cytotoxicity in never-medicated schizophrenic inpatients will permit further exploration of the association between immune alterations and schizophrenia.

Methods

Subjects The 36 subjects who were included in this study consisted of four groups of men-hospitalized patients with depression (n = 10), control subjects who were age and dayof-assay matched to the depressives (n = 10; controls l), schizophrenic inpatients (n 8), and controls age and day-of-assay matched to the schizophrenics (n - 8; controls ll). Testing of all subjects was conducted between March 1988 and March 1990. Values of NK activity in this sample have not been previously reported except for one controldepressed patient pair (Irwin et al 1990a, 1990b). The inpatients with major depression were recruited from the UCSD-Mental Health Clinical Research Center (MHCRC) at the San Diego Veterans Affairs Medical Center (VAMC) (J. Christian Gillin, M.D., Director). The MHCRC admits depressed patients who are veterans (including those who are indigent or able to provide co-payment) for inpatient treatment of either acute or severe, chronic affective illness. All depressed patients were interviewed by a psychiatrist using the Schedule for Affecfive Disorders and Schizophrenia (SADS) and met DSM-III-R criteria for major depression (APA 1987). The depressives were free of any medical disorders known to affect immune function and were not included if they had received any psychotropic medication during the previous 2 weeks. Indeed, seven depressives were free of psychoactive medications for greater than 3 months, while the other three patients had undergone a drug washout period lasting either 15, 19, or 60 days. The hospitalized schizophrenic patients consisted of men who were admitted to a ~.~,,..w.~.~. l a O T , . , a ~ l ~ u l ~ .

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participating in a study of late-onset schizophrenia (D. Jeste, M.D., investigator). Although the schizophrenic syndrome seen in the late-onset patients is similar but not identical with that seen in younger patients (Jeste et al 1988), this study recruited schizophrenic patients with late onset (over age 45) to yield a schizophrenic patient group whose mean age was comparable to that of the depressives since age is a known correlate of immune function (Schleifer et al 1989). All schizophrenic subjects were interviewed using the Structured Clinical interview for DSM-III (Spitzer and Williams 1983) and met DSMi|l-R criteria for Schizophrenia, Paranoid Type (APA 1987); none fulfilled criteria for either an affective or schizoaffective disorder. Diagnosis of schizophrenia, paranoid type, was confirmed by ongoing clinical evaluation for 6 months to 2 years after the admission interview and testing. All schizophrenic patients were free of acute and chronic medical disorders associated with alterations in immunity, and were not taking drugs known to affect immune function. Furthermore, since all of the schizophrenic patients were in the midst of their first ~iagnosed psychotic episode, none of the schizophrenics had ever been medicated for psychosis. Medication-naive status was corroborated by interviews with a

Killer Cell Cytotoxicity in Psychoses

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1 ! 33

resource person (i.e., a family member or friend) and by review of ~ c a l records. One schizophrenic patient had received a single dose of chloral hydrate 5 days before testing. Separate control groups were studied for each experimental group. These ~ p i talized controls were recruited from the San Diego area using a standarch'zed search strategy and were matched in terms of age ( "*-i0 years) and gender with either a depressed patient or a schizophrenic subject who was being tested on the experiment day. All of ~ controls met Research Diagnostic Criteria (RDC) for Never Mentally I11 (Spitzer et al 1978), were free of any acute or chronic medical disorders, and were not using any psychotropic medications.

Procedures Each subject and matched control were studied on the same day and at the same time of day. Severity of depressive symptoms was evaluated on the day of testing (by CC) using the 17-item Hamilton Depression Rating Scale (Endicott et al 1981). Between ~ and 1000 hr, !0 ml of blood was collected by venipuncture into a heparinized vacutainer. All assays of NK activity were performed on freshly drawn blood samples by |aboratory personnel blind to the clinical status of patients and control subjects. A Coulter counter S + 4 was used to obtain total white blood cell count. Pefiphe~ blood lymphocytes and differential cell counts were manually counted by an American Society of Clinical Pathology certified hematology technician w i ~ 2 hr of sample draw using a blood smear stained by modified Wright's solution. Assay of ~ cell activity involved the sedimentation of mononuclea.- cells on FicoH-Hypaclue (Pharmacia, NJ) (Irwin et al 1987b). Cells were collected at the interface and washed twice with phosphate-buffered saline, yielding a cell suspension that was greater than 99% viable with less than 5% monocytes by Wright's stain (Bloom et al 1983). Cells were suspended in RPMI with 10% fetal calf serum at a concentration of 2 x 106 cells per milliliter and incubated with 5~Cr-labeled K-562 target ceils at effector-to-target (E:T) cells ratios of 40: ~ 20:1, 10:1, and 5:1 in triplicate. Following 3 hr of incubation in a 37°(: incubator with 5% CO2, the plate was removed and spun at 200 g. An aliquot (100 ttl) was removed and chromium release was measured in a gamma counter. Assay results for NK activity were expressed as percentage specific cytotoxicity across the four effector-to-target-cell ratios (Irwin et al 1990a) and as lytic units (Irwin et al 1990a).

Statistical Analysis To test for differences between the depressed patients and their age-, gender-~ and dayof-assay-matched controls (controls I) and between schizophrenic inpatients and their matched controls (controls H), paired t-tests were used. Results Table I summarizes age, severity of depressive symptoms, an_dthe i_rnmuno!ogic varifies in controls I and the depressed patients. Mean age was similar in the two groups, consistent with the age-matching procedures employed. Severity of depressive symptoms as measured by the Hamilton score was significantly higher in the depressives than in the control subjects. NK activity was significantly (/7 < 0.01) lower in the depressives as compared

1134

C . L Caldwell et al

BIOL PSYCHIATRY 1991.30:1131-1138

Table !. Age, Depression Scores, and Immune Function in Controls ! and the Depressed Patients Controls I Measure

Mean (SD)

patients 10) Mean (SD)

Age Depression scores Natural killer cytotoxicity (lyric units) Total ieukocytes" Neutrophil numbers° % cells Lymphocyte numbers° % cells Monocyte numbers° % cells

44.8 (12.2) 0.8 (I.I) 16.3 (! 1.5)

45.6 (12.5) 14.0 (4.5) 8.7 (8.7)

0.1 9.0 3.1

0.9 0.001 0.01

4.9 (0.8)

7.8 (2.9)

3.2

0.01

2.7 (0.7) 57.4 (12.0)

4.8 (2.3) 60.2 (7.2)

2.8 0.6

0.01 0.6

! .5 (0.6) 31.4 (10.0)

2.2 (0.8) 29.6 (5.5)

2.4 0.5

0.03 0.6

0.4 (0.2) 8.3 (3.5)

0.4 (0.1) 5.7 (!.8)

0.3 2.1

0.8 0.6

(n =

10)

(a =

,,

p

~Cells x 103 microliter of blood,

with the controls (Figure l). Quantitative measures of immunity including total white blood cells and absolute numbers of neutmphils and lymphocytes were significantly higher in depressives than in the controls, although percentages of neutrophils, lymphocytes, or monocytes did not differ between the two groups (Table 1). Table 2 shows the mean values of age, depression scores, and immune variables in

o--o SO

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I

Controls

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A--.---4L ControL~

i t0

o

IL

l=

A - - A S(:~4hmah: P~lents

20-

10

; I I I 40:.1 20:1 10:1 5:1 E]rI~CTOR TO TARGLrTCELL RATIO

o

; 40:1

t ! I 20:1 10:1 5:1 E]FTI[CTOR TO I ~ L : ' T CELL RATIO

Figure 1. Natural killer cell activity across the four effcctor-to-target cell ratios in controls ! (o) and hospitalized depressed subjects (e) and in controls ILl (A) and hospitalized schizophrenic patients (A). Each point represents mean specific cytotoxicity _ SEM.

Killer Cell Cytotoxicity in Psychoses

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1135

Table 2. Age, Depression Scores, and Immune Function in Controls II and the Schizophrenic Patients

sc~~ Conuols I (n 8) Mean (SD)

~ts (n 8) Mean (SD)

t

45.9 (16.2) 1.6 (I .5) 17.6 (13.3)

41o9 (18.6) 7.9 (7.5) 14.0 (I I.I)

0.5 2.2 0.7

0o7 0.07 0.5,2

(0.8)

1.7

0.13

3.1 (0.7) 60. I (9.1)

1,7 0.6

0.13 0.56

=

Measure Age Depression scores Natural killer cymtoxicity (lyricunits) Total leukocytes" Neum)phil

numbe~ % ceils

7.3 (3.4) 4.7 (2.6) 63.6 (9.7)

=

5.1

Lymphocyte numbe~ % cells Monocy~

!~5 (0.5)

1.0

0.35

26.5 (I0.0)

1.8 (0.8)

28.46 (0.9)

0.4

0.70

0.4 (0.2) 6.4 (2.6)

0.3 (0.2) 6.1 (4.I)

0.8 0. I

0.42

numbers"

% cells

0.~

"Cells x 103 microliter of blood.

the controls 11 and the schizophrenic patients. The two groups ~ d not differ in age, depressive symptoms, or the immune variables. NK activity was s ~ a r in the schizophrenics and controls (Figure 1). The relationship between severity of depressive symptoms and NK activity was examined by correlating Hamilton scores with values of lyric activity. In the total sample, Hamilton scores were significantly negatively correlated with NK activity in l ~ c wits (r = - 0 . 2 8 , p < 0.05). In addition, a similar negative correlation between Hamilton scores and NK activity was found within t,he depressed patients (r = - 0 . 5 0 , p = 0.07), but not in the schizophrenics or either of the control groups.

Discussion The present study suggests that NK activity is reduced in men hospitalized with major depression, consistent with our previous findings using larger samples (Irwin et al 1990b). In contrast, schizophrenic inpatients had values of cytotoxicity that were similar to those in the controls, and it appears that hospitalization on a psychiatric unit does not in itseff produce a reduction in NK cell activity. Although these cautious conclusions require replication in a larger sample, our findings of reduced NK activity in depression but not in schizophrenia exte;ld previous work that has demonstrated a relationship between reduced cytotoxicity and severity of depressive symptoms. The finding of reduced NK activity in hospitalized male depressed patients may not . . . . . . . . . . . ,,. . . .=~,h....,,..,,.. ........... .,,.,,,,~ni.o with .,,o;,,,,l,..,..,.c¢;,,., .....j . . . . r . . . . . . . . . . .,,,, . . . .~m~.do,,,r,, . ., 'l~pressiv"~. For ex~_mp!e. in studies of cellular irmnunity in depression that included men and women as well as outpatients and inpatients (Schleifer et al 1959). no significant differences in NK activity or in lymphocyte responses to mitogen stimulation have been found. It is possible that in vitro measures of cellular immunity are more likely to be altered in men than women,

1136

BIOL PSYCHIATRY 1991;30:I131-I 138

C.L. Caldwell et al

consistent with ~eclinical observations of sex-related differences in immune function (Grossman 1984). In addition, severity of depressive symptoms negatively correlates with NK activity (Irwin et al 1987a, 1990b) and ambulatory depressives may be less severely depressed than hospitalized depressives, ,although a reduction on NK activity was found in this study despite the inclusion of some depressed patients who were only modestly depressed. The increase in total leukoc~s and numbers of neutmphils in the depressed patients as compared with the controls confirms the results of previous reports (Kronfol et al 1984; Irwin et al 1987a; 1990a, 1990b; Darko et al 1988b; Kronfol and House 1989; Targum et al 1989). Although the mechanism by which the numbers of leukocytes and neutmphils is increased in depressed patients remains unexplored, circulating numbers of neutmphils have been associated with plasma concentrations of cortisol in depression (Kronfol et al 1989; Targum et al 1989), suggesting that glucocorticoids may contribute to leukocyte changes or redistribution of these cells into the peripheral circulation. Never-medicated schizophrenic patients do not appear to show a reduction of cellular immunity as measured by NK activity, and it is likely that some of the alterations in immune function that have been reported in other studies may be due to the effects of currel~t or past administration of neuroleptic medication (Ferguson et al 1975; Zatrabi et al 1979; Kerepcic and Jurin 1983). For example, with regard to NK activity, Urch et ai (1988), Delisi et ai (1983), and Schindler et al (1986)reported a reduction of cytotoxicity in schizophrenia but included schizophrenic patients who had either been previously medicated or were currently treated with neuroleptic medications. Finally, unlike the present study, none of the previous studies of NK activity in schizophrenia utilized an age-matched pair design. Nevertheless, despite the lack of difference in NK activity between paranoid schizophrenics and controls, studies have preliminarily found changes in cytotoxicity in other diagnostic subgroups of schizophrenics (Kronfol et al 1990) and schizophrenia-associated changes in other measures of immunity such as decrease¢o IL-2 production (Ganguli et al 1989), increased circulating IL-2 receptors (Rapaport et al 1989), or elevated CD5 lymphocytes (McAllister et al 1989). The decrement in cytotoxicity in depression may he due to a selective loss or redistribution of lymphocytes such as NK cells. For example, Evans et ai (1988) found that circulating NK phenot~ves are reduced in major depression, in contrast with Darko et al (1988a), who found no depression-related reduction on NK cell numbers, and the present study, which reports an increase in the number of circulating lymphocytes. However, regardless of whether NK cell number is altered in depression, NK activity is not correlated either with number of lymphocytes (data not shown) or number of NK phenotypes in depression (Evans et al 1990), suggesting that reduced NK cytotoxicity cannot he solely explained by a decrease in circulating numbers of NK cells. In summary, this present study has suggested a decrement in NK cell activity in men hospitalized with depression but not in those inpatients with schizophrenia. Depression° related reduction in NK activity does not appear to be due to the nonspecific effects of hospitali_zation stress. Further research is needed to replicate these data and to establish the biological mechanisms that produce changes in measures of cellular immunity such as NK activity in depression. "12:,is work was supported by the San Diego Veterans Affairs Medical Center VA Merit Review, the NIMH Mental Health Clinical Research Center Grant (MH30914), and NIMH grant MH44275-01 to M. Irwin.

Killer Cell Cytotoxicity in Psychoses

ega. PsYcmATav ts~t~tt3t-tt~

1137

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