Delineation of suppressor and helper activity within the OKT4-defined T lymphocyte subset in human newborns

Lymphocytes taken from the cord blood of newborns have active suppressor activity. Using in vitro PWM-stimulated cocultures, unfractionated T cells from newborns potently suppressed the expected immunoglobulin G (IgG) synthesis of their mothers' peripheral blood lymphocytes (PBL). Using positive and negative selection techniques, we characterized the active suppressor cell as expressing the OKT4+T8- phenotype. This cord blood lymphocyte subset suppressed maternal IgG synthesis after depletion of maternal suppressor cells, implicating the ability of newborn T cells to suppress directly rather than by inducing adult suppressor activity. Sublethal amounts (1500 rad) of gamma-irradiation fully abrogated the suppressor activity of cord blood T lymphocytes. Radioresistant cord T cells provided T cell help. Irradiation of cord OKT4+ and OKT8+ populations and their subsequent culture with maternal B cells determined that helper activity was a radioresistant subpopulation of the OKT4+ subset. These results indicate significant differences in the functional properties of T cell subsets from adults and newborns. Population studies determined that cord blood lymphocytes had a greater proportion of OKT4+ cells and lower proportion of OKT8+ cells than PBL from unrelated adults. The mothers tested had similar proportions of OKT4+ cells as their babies, and these levels are significantly higher than those of unrelated adults.     

Evaluation of the circulating and splenic lymphocyte subpopulations in patients with non-Hodgkin lymphomas and Hodgkin's disease using monoclonal antibodies

The number of B lymphocytes, T lymphocytes and their helper/inducer, cytotoxic/suppressor and NK/K subpopulations was measured in peripheral blood and spleen cell suspensions from patients with Hodgkin's disease (HD) in the active stage of the disease and in remission status, as well as in Non-Hodgkin lymphomas (NHL) in active stage of the disease. B lymphocytes were determined by direct immunofluorescence and T lymphocytes with the E rosette technique. Helper/inducer, cytotoxic/suppressor, and NK/K T lymphocytes were determined by indirect immunofluorescence with the monoclonal antibodies OKT4, OKT8 and Leu 7 (HNK1). In the same way, Lyt3 was used for determination of the total T lymphocytes. Whereas in peripheral blood of the NHL group an increase of B lymphocytes and a slight reduction of T lymphocytes could be observed, with normal distribution of the subpopulations, in patients with active HD as well as in those in remission, a marked absolute and relative decrease of T helper/inducer cells was found with normal cytotoxic/suppressor and NK/K proportion. In contrast to this, a significant increase of helper/inducer T lymphocytes with decreased cytotoxic/suppressor T proportion was found in spleen cell suspensions of patients with HD.     

T lymphocyte subsets in patients with malignant melanoma

Summary T lymphocyte subset profiles were determined by monoclonal antibodies on cryopreserved peripheral blood lymphocytes from 57 patients with malignant melanoma and 19 healthy controls. Quantitation of percentages of total T cells (OKT3.PAN), helper (OKT4.IND) or suppressor (OKT8.SUP) cells, and the ratio of helper/suppressor subsets revealed no correlation of these markers with stage of disease or clinical outcome. A sequential study of these markers on peripheral blood lymphocytes from three stage I melanoma patients with subsequent recurrent disease showed no fluctuations that could be correlated to tumor progression. This study indicates that there is no systemic imbalance in T cell subsets in malignant melanoma and that quantitation of these subsets cannot predict the clinical course of this disease.     

TPA, tumor promoter-induced suppression of immunoglobulin secretion in human blood lymphocytes

12-O-Tetradecanoylphorbol-13-acetate (TPA) modulates DNA synthesis and differentiation of normal and malignant human lymphoid cells. Using the reverse plaque forming assay and radioimmunoassay, we showed that nontoxic concentrations of TPA (5 to 10 ng/ml) inhibited Ig secretion of peripheral blood lymphocytes. This inhibition was dependent on T lymphocytes and not monocytes; TPA treatment of the B cell-enriched fraction slightly enhanced Ig secretion. Suppression was evident when the proportion of TPA-pretreated T lymphocytes exceeded 50%. TPA-induced suppressor cells were present in both OKT8+ (suppressor/cytotoxic) and OKT4+ ("helper/inducer") subpopulations. The suppression was diminished but not abolished by the irradiation of T lymphocytes. In addition, TPA treatment modulated the expression of OKT4 antigen, whereas the expression of OKT8, 9.6 (sheep erythrocyte receptors) and surface Ig remained unchanged. Modulation of OKT4 was energy dependent and was not blocked by a maximal saturation of TPA receptors at 4 degrees C. We postulate that TPA-induced suppression of Ig secretion is T cell dependent and is likely to be associated with proliferation and activation of OKT8+ and OKT4+ lymphocytes and the induction of OKT4+ suppressor cells.     

Glucocorticoid receptors in subpopulations of human lymphocytes defined by monoclonal antibodies

Glucocorticoid receptors (GR) were investigated in subpopulations of lymphocytes identified by monoclonal antibodies. Purified T (OKT3+) and non-T lymphocyte subpopulations were isolated from human peripheral blood using Degalan bead columns coated with rabbit anti-human IgG. Purified subpopulations of OKT4+ and OKT8+ lymphocytes were obtained by coating the nonadherent population (T cells) from the first column with OKT4+ or OKT8+ and pouring it into a second Degalan column, coated with goat anti-mouse IgG. GR content and affinity were analyzed by a whole cell assay with [3H]dexamethasone as tracer. The numbers of GR in lymphocyte subpopulations (OKT3+ cells, non-T cells, OKT4+, and OKT8+ cells) were nearly equal. It is concluded that the differential effects of glucocorticoids on the circulatory kinetics of OKT4+ and OKT8+ cells probably are not related to differences in glucocorticoid receptors of these T-cell subpopulations.     

T lymphocyte subpopulations and lymphocytotoxic antibodies in patients with autoimmune haemolytic anaemia

Evaluation of T lymphocyte subpopulations was performed on peripheral blood of patients affected by idiopathic or associated autoimmune haemolytic anaemia. A marked reduction of absolute number of T gamma and T mu cells was observed in 11 of 16 patients; a decrease of both OKT4+ and OKT8+ cells was found in 8 of 10 patients. Circulating cytotoxic antibodies against autologous and allogenic T lymphocytes and/or thymocytes were found in almost all the cases. T lymphocyte subsets depletion, probably connected to antibodies against T lymphocytes and their thymic precursors, could play a role in autoimmunity because of T3+/T4+ cell depletion.     

A defect in the suppressor circuits among OKT4+ cell populations in patients with systemic lupus erythematosus occurs independently of a defect in the OKT8+ suppressor T cell function

The autologous mixed lymphocyte reaction (MLR) is thought to be part of a regulatory role of T cells on B cell function. OKT4+, but not OKT8+, cells can proliferate in response to autologous non-T cells. Moreover, the OKT4+ cell population activated early in the course of autologous MLR functioned as inducer cells for the differentiation of B cells, whereas later in the response, the activated OKT4+ cells were particularly enriched in suppressor cells. A part of the autologous MLR appears to be an important pathway for the activation of feedback suppression mechanisms among cells contained within the OKT4+ populations. Patients with systemic lupus erythematosus (SLE) were studied with regard to the following OKT4+ cell functions in vitro after activation in the autologous MLR: a) proliferative response, and b) helper and suppressor activities for differentiation of B cells. A marked reduction in the proliferative response of OKT4+ cells was observed in SLE patients. SLE OKT4+ cells activated in the autologous MLR could function as helper cells but could not exert any suppressor activity. This OKT4+ cell abnormality was present regardless of the disease activity, and occurred in the absence of autoantibodies including anti-T cell antibodies. Instead, SLE anti-T cell antibodies could preferentially eliminate cells bearing the OKT8+ phenotype characteristic of suppressor cells in populations of normal T cells. These results suggest that the defect in the suppressor circuits among OKT4+ cell populations is intrinsic to SLE lymphocytes and that the OKT8+ suppressor T cell defect is caused by antibodies produced by the B cells of SLE patients.     

Regulation of immunoglobulin production in human peripheral bood leukocytes: cellular interactions.

The intercellular influences regulating immunoglobulin (Ig) synthesis by normal human peripheral blood leukocytes (PBL) were investigated in cells stimulated by pokeweed mitogen (PWM). This system was shown to be totally T lymphocyte dependent as purified B lymphocytes (less than or equal to 1% T lymphocytes) failed to make significant amounts of Ig. No evidence was obtained for an Ig class switch as all classes of Ig (IgM, IgG, IgA) were shown to be produced in increasing amounts over a 6-day time period. T lymphocytes demonstrated maximum helper effect when mixed with equal numbers of B cells. This helper effect was mediated through the dual mechanisms of increasing the number of B lymphocytes containing cytoplasmic Ig and by increasing the maturity of these B lymphocytes as demonstrated by an increasing Ig production per B lymphocyte. When present in higher numbers, T lymphocytes were also capable of suppressing Ig production. This T-mediated suppression was first evident as a decrease in the Ig produced per B lymphocyte (decreased maturity). With maximum T suppression Ig-containing B lymphocyte numbers were also diminished. T lymphocyte help was relatively independent of macrophages (phagocytic cells) and did not require DNA synthesis for expression. Both T help and suppression were shown to cross allogeneic barriers. Immature T lymphocytes (thymocytes) were incapable of mediating either activity. Normal human PBL contain T lymphocytes campable of mediating both T help and suppression and the Ig produced by PBL was shown to be the balance of these activities. This balance probably represent the participation of distinct T lymphocyte subpopulations analogous to the T helper (Ly 1+) and T suppressor (Ly 2+, 3+) populations in the mouse.     

Secretions of anti-myelin-associated glycoprotein antibodies by B cells from patients with neuropathy and nonmalignant monoclonal gammopathy

Four patients with peripheral neuropathy and nonmalignant monoclonal gammopathy with anti-myelin-associated glycoprotein (MAG) antibodies were studied to determine whether secretion of anti-MAG IgM antibodies by B cells was autonomous, or whether the monoclonal B cells were responsive to T cells. Secretion of anti-MAG IgM by isolated B cells was stimulated by the addition of increasing numbers of pokeweed mitogen (PWM)-activated autologous OKT4+ helper T cells in all four patients. Secretion of anti-MAG IgM by peripheral blood lymphocytes was dependent on the ratio of OKT4+ T helper cells to OKT8+ T suppressor/cytotoxic cells. In three patients with an OKT4+ to OKT8+ T-cell ratio of 2:1, PWM activation stimulated secretion of anti-MAG IgM; in one patient with an OKT4+ to OKT8+ ratio of 1:2, activation by PWM suppressed anti-MAG IgM secretion. These studies suggest that the monoclonal B cells that secrete anti-MAG IgM are responsive to regulatory T cells.     

Chemoattractant lymphokines specific for the helper/inducer T-lymphocyte subset

The cellular content of T-lymphocyte-rich inflammatory sites is dependent in part on the in situ elaboration of chemoattractant factors. We have previously described three T-lymphocyte-specific chemoattractant lymphokines; a chemokinetic factor, lymphocyte chemoattractant factor (LCF, MW 56,000), and two distinct lymphocyte migration inhibitory factors (LyMIF75K, MW 75,000; and LyMIF35K, MW 35,000). These factors are produced by human T cells in response to antigen, concanavalin A, or histamine stimulation. In this communication, we report that LCF and LyMIF35K are produced by OKT8+ (suppressor/cytotoxic) and OKT4+ (helper/inducer) lymphocytes, respectively, and are selectively chemoattractant for the OKT4+ lymphocyte subset. LyMIF75K is produced by OKT4+ cells and inhibits both OKT4+ and OKT8+ lymphocyte migration. Production of LCF and LyMIF35K by infiltrating lymphocyte subsets may be one mechanism whereby unactivated helper/inducer T lymphocytes are selectively recruited to sites of inflammation.     

Lymphocyte subpopulations in the neonate: identification of an immature subset of OKT8-positive, OKT3-negative cells

T cell subpopulations of lymphocytes from cord blood (CBL) of 24 newborns and from peripheral blood (a-PBL) of 24 healthy adult volunteers were assessed in T cell-enriched, T cell depleted and unseparated lymphocyte fractions by using OKT3, 4, 6, and 8 monoclonal antibodies. The results show that T cell-enriched CBL include adult numbers of OKT3+, OKT4+, OKT6+ and OKT8+ lymphocytes whereas the T cell-depleted fraction consists of a high percentage of OKT8+, OKT3-, non-E rosette-forming cells bearing a PNA receptor. The presence of the PNA receptor and the lack of the OKT3+ antigen strongly support the hypothesis that the subset of OKT8+ cells in cord blood includes immature T lymphocytes that may represent an intermediate stage between thymocytes and mature peripheral T cells.     

In vitro selective effect of melphalan on human T-cell populations

Summary In vitro treatment with 2 g/2×10⁶ cells melphalan (l-PAM: l-phenylalanine mustard) significantly decreased the total number of T lymphocytes from peripheral blood (PBL) of healthy human donors and of the OKT₄ population (precursor suppressor/helper/inducer) T cells as defined by monoclonal antibodies OKT₃ and OKT₄, respectively. No changes in the OKT ₈ ⁺ lymphocyte population (cytotoxic/mature suppressor cells) were observed following the same treatment. Preincubation of PBL with l-PAM at concentrations that do not affect the rate of DNA synthesis in PHA-stimulated lymphocytes inhibited the generation of T suppressor lymphocytes by ConA, as shown by their effect on PHA stimulation. Treatment of allogeneic PBL with l-PAM had no effect on mature suppressor T cells already induced by Con A, as shown by incubation of PBL with l-PAM after incubation with ConA.     

Functional analysis of monkey lymphocyte subsets defined by OKT4 and OKT8 monoclonal antibodies

The percentages of rhesus monkey blood lymphocytes (PBL) reactive with OKT4 and OKT8 antibodies and the $\text{OKT}\text{4}\text{OKT}\text{8}$ ratio showed significant correlations with the log of the immunoglobulin plaque-forming cell (PFC) response after stimulation with pokeweed mitogen (PWM). These correlations suggested that monkey OKT4⁺ cells function as “helper” cells and OKT8⁺ cells function as “suppressor” cells for the PFC response. This was confirmed by separation and study of enriched T- and B-cell subpopulations. OKT8-depleted (OKT4⁺) and OKT4-depleted (OKT8⁺) cells were obtained by treatment of purified T cells with antibody and complement. OKT4⁺ cells augmented the PWM-induced B-cell differentiation into PFC but OKT8⁺ cells did not. OKT8⁺ cells suppressed the PFC response by mixtures of B cells and OKT4⁺ cells. OKT8 antibodies also detected a suppressive cell subset in African green monkeys since the percentage of OKT8⁺ cells showed a negative correlation with the log PFC response. OKT4 antibodies failed to bind to African green monkey PBL.     

Radiosensitivity of CD4 or CD8 positive human T-lymphocytes by an in vitro colony formation assay

The recent development of an in vitro lymphocyte colony assay makes it possible to examine variations in the radiosensitivity of humans using peripheral blood lymphocytes (PBL) instead of the skin fibroblast assay. Our recent study (M. Hakoda et al., Mutat. Res. 197, 161-169, 1988) showed that most of the colonies consisted of lymphocytes bearing CD4 or CD8 antigens. Since the fraction of CD4+ and CD8+ cells in PBL differs among individuals, we suspected that individual radiosensitivity might be biased by the different subset frequencies if the dose-survival curves of the CD4+ and CD8+ cells were different from each other. In the present study, CD4+ (helper/inducer T) and CD8+ (suppressor/cytotoxic T) lymphocytes were isolated from PBL and their dose-survival curves were determined. The results showed that the D10 (dose required to reduce the surviving fraction to 10%) was similar for these two types of cells [3.13 +/- 0.10 Gy (mean +/- SD) for CD4+, 3.34 +/- 0.50 Gy for CD8+ and 3.14 +/- 0.17 Gy for the unsorted cells], supporting the use of the whole PBL population for the screening of individuals with altered radiosensitivity.     

Systemic administration of autologous,alloactivated helper-enriched lymphocytes to patients with metastatic melanoma of the lung

Summary A phase I study was carried out to test the feasibility and toxicity of infusing large numbers of autologous, alloactivated helper lymphocytes into patients with metastatic melanoma. Patient peripheral blood lymphocytes (Pt-PBL) obtained by lymphopheresis and expressing the helper phenotype BT5/9 were separated and stimulated for 48 or 72 h with a pool of PBL from four to six healthy donors. Patients were then infused with such activated lymphocytes over a 2–3 h period. A total of 4 phereses and infusions (2/week for 2 weeks) were carried out for each cycle in each patient. Of the five patients treated, two received a second round of infusions. Infusion of autologous PBL stimulated in vitro for 48 h caused chills, fever, headache, and increased blood pressure. All symptoms disappeared in 2–3 h and were easily controlled by appropriate therapy. When lymphocytes were given after 72 h of allostimulation, no or very mild toxicity was observed. Serum chemistry, coagulation, autoimmunity, and urine analysis showed no gross abnormalities during therapy or follow-up of the patients. Immunological parameters (OKT4/OKT8 ratio, NK activity and cytotoxic T cell activity to autologous melanoma) were evaluated before starting the therapy, during its course and during the 3 to 6 months follow-up. The OKT4/OKT8 ratio increased significantly but transiently soon after the first course of infusions in one of the two patients tested. NK activity increased after 75–100 days in the three patients tested and in one of them it was high even after 180 days. No correlation between NK activity and prognosis was apparent. Cytotoxicity to autologous tumor was assessed in two patients, only one of whom exhibited an increased activity from 75 to 180 days, which was associated with a prognosis better than that of the negative patient. Five patients were treated: two had progressive disease, two had stable disease for 5 and 6 months, respectively. In the first of these patients, a new cycle of lymphocyte infusions was carried out which caused a measurable reduction of lung tumor nodules whose growth, however, resumed 4 months later. This patient died 14 months after the onset of therapy. The fifth patient had a partial regression of pulmonary and intracranial metastases after therapy, but eventually died 3 months later. These results indicate that infusion of a high numbers of autologous, allostimulated helper PBL is a feasible and safe procedure, which could therefore be used in future studies of adoptive immunotherapy of cancer.     

Further characterization of mitogen-induced autorosette-forming cells: correlation with T-cell subsets and with lymphocyte proliferative responses to mitogens

Spontaneous autologous rosette-forming cells (ARFC), which form rosettes with autologous erythrocytes, have been of interest as a subset of thymus-derived lymphocytes (T cells). An association of these cells with concanavalin A (Con A)-induced ARFC has been suggested. Furthermore, the Con A-induced ARFC have been shown to be a suppressor T-cell subset in the Con A-generated suppressor system. We have previously reported the induction of ARFC from T cells by several T-cell mitogens such as phytohemagglutinin-P (PHA) and allogeneic non-T cells other than Con A. In the present report, we further characterized the mitogen-induced ARFC and have extended the study to patients with systemic lupus erythematosus (SLE). We have found that ARFC are also inducible from peripheral blood T cells by pokeweed mitogen (PWM). Studies of T-cell surface markers on the ARFC using OKT monoclonal antibodies confirmed the induction of ARFC from both OKT4- and OKT8-reactive T cells by either Con A, PHA, or PWM stimulation. However, OKT4-reactive T cells were the major cellular source of the ARFC induced by all of the mitogens. In studies of SLE patients, proportions of both Con A- and PWM-induced ARFC were found to be significantly low in PBL of SLE patients treated with moderate or large doses of prednisone, with or without concomitant immunosuppressants, but not in SLE patients without such treatment. Proportional analysis of the T cells and their subsets suggested association of these alterations in the mitogen-induced ARFC with the OKT4-reactive T cells, since a significant decrease in the OKT4-reactive T-cell subset was demonstrated in the PBL of these patients. Proportions of PHA-induced ARFC, however, were not significantly different between SLE patients and healthy adults. Moreover, positive correlations of the mitogen-induced ARFC with lymphocyte proliferative responses to each mitogen were established in both SLE patients and healthy adults. These results further support our previous observation that suggest the receptors for autologous erythrocytes are enhanced or reexpressed on those T cells which are highly activated by mitogens.     

Immunologic findings in healthy Haitians in Montreal

To investigate the occurrence of acquired immune deficiency syndrome in Haitians, a health status questionnaire was administered and selected studies of immune status done in a randomly chosen sample of 189 healthy adult Haitians living in Montreal. The study group was comparable to a large sample of Haitians in Montreal interviewed in the 1981 census with respect to age, sex, number of persons per household and year of immigration, but the proportion of currently married people in the study was larger (60.8% v. 42.6%). The results in the study group were compared with those in a sample of 189 non-Haitians matched for age, sex and neighbourhood of residence. Persons with known causes of impaired immune function were excluded. The participation rate was 87.5%. The study and control groups both reported few symptoms and chronic health problems and had comparable demographic data, including rate of employment and income. The mean total numbers of lymphocytes, OKT3 and OKT4 (helper) and OKT8 (suppressor) cells were significantly higher in the Haitians than in the controls, though still within normal limits. There was a borderline elevation of the lymphocyte response to phytohemagglutinin in the Haitians. The ratios of helper to suppressor T cells in the two groups were, however, not significantly different. The Haitians, in comparison with non-Haitians living in the same community, had no demonstrable abnormalities of cellular immune function.     

Interferon is the suppressor of hematopoiesis generated by stimulated lymphocytes in vitro

Lymphocytes that inhibit hematopoiesis may have a pathogenic role in some forms of bone marrow failure, and lymphocyte-mediated suppression may also be important in the normal regulation of bone marrow function. We have investigated the mechanism of in vitro suppression of hematopoiesis by T cells by using the methylcellulose colony culture system. Total peripheral blood T cells and separated subpopulations of helper (OKT4+) and suppressor (OKT8+) cells that have been stimulated by exposure to lectin suppress autologous colony formation by bone marrow myeloid (CFU-C) and erythroid (BFU-E) progenitor cells. Medium conditioned by these cells is also inhibitory, indicating that the suppressor activity is a soluble factor. A strong correlation existed for the concentration of interferon and the degree of hematopoietic suppressor activity in these supernatants; both activities peaked at days 3 to 5 of incubation and had sharply declined by day 7. Interferon production was enhanced by exposure of lymphocytes to sheep red blood cells during the rosetting procedure. Specific antiserum and a monoclonal antibody directed against gamma-(immune) interferon abrogated the inhibitory activity for hematopoiesis produced by lectin-stimulated T cells; an antiserum to alpha-interferon was generally much less effective in neutralizing activity. We infer from these results that gamma-interferon is the mediator of hematopoietic suppression generated by lectin-treated T-cells.     

Characterization of recirculating lymphocytes in rheumatoid arthritis patients: selective deficiency of natural killer cells in thoracic duct lymph

Five patients with rheumatoid arthritis (RA), who were treated by lymphocyte depletion by using thoracic duct drainage (TDD), provided an opportunity to characterize the phenotype and function of their recirculating lymphocytes. We found that: a) thoracic duct lymphocytes (TDL) were similar in their proportion of T cells (83% +/- 6 OKT3+), OKT4+ subset (65% +/- 8), and OKT8+ subset (22% +/- 6) to peripheral blood lymphocytes (PBL): b) fewer natural killer-like cells were present in TDL (5% +/- 4 Leu-7+; 2% +/- 2 Leu-11+: 8% +/- 2 OKM -1+) than in PBL (20% +/- 10 Leu-7+: 11% +/- 6 Leu-11+; 18% +/- 5 OKM -1) (p less than 0.01); c) TDL differed from synovial fluid lymphocytes ( SFL ) and synovial membrane lymphocytes ( SML ) in that TDL lacked a high percentage of activated lymphocytes (T cells bearing Ia antigen, OKT10 , and transferrin receptor): d) immature T cells (expressing either OKT6 antigen or reactive with peanut agglutinin) were not found in TDL even late in the course of TDD: and e) in vitro functional studies demonstrated that TDL were similar to PBL in their ability to synthesize immunoglobulin after mitogen stimulation and to generate cytotoxic T lymphocytes capable of lysing autologous EBV-transformed B cells. However, natural killer activity, as measured by lysis of K562 cells was significantly lower in TDL than PBL (p less than 0.05). These results demonstrate that natural killer cells defined by phenotype and function are excluded from thoracic duct lymph and thus have a circulation pattern different from most T cells.     

Predominance of helper-inducer T cells in mesenteric lymph nodes and intestinal lamina propria of normal nonhuman primates

To define the characteristics of T cells associated with the gastrointestinal tract, the phenotypes and immunoregulatory function of T cells from mesenteric lymph node (MLN) and lamina propria lymphocytes (LPL) were compared to peripheral blood (PBL) and spleen lymphocytes in normal nonhuman primates. Mesenteric lymph node lymphocytes were characterized by a higher proportion of Leu-3+(CD4+) and 9.3+(alpha-Tp44) lymphocytes and a lower proportion of Leu-2+(CD8) lymphocytes than lymphocytes in other sites. LPL and MLN lymphocytes were both characterized by a higher proportion of cells having the helper-inducer phenotypes (Leu-3+, Leu-8+, Leu-3+, 2H4+) compared to PBL. A lower proportion of cells with the suppressor-inducer phenotypes (Leu-3+, Leu-8+, Leu-3+, 2H4+) was found in LPL, but not in MLN lymphocytes compared to PBL. In studies of the Leu-2+ T cells, it was found that whereas PBL, spleen, and LPL contained approximately equal proportions of Leu-2+, Leu-15+ (suppressor phenotype) and Leu-2+, 9.3+ lymphocytes (cytolytic T-cell phenotype), the MLN T cells were predominantly Leu-2+, 9.3+. Furthermore, the Leu-3/Leu-2 ratio was significantly higher in MLN compared to other sites. In pokeweed mitogen-stimulated cultures, the highest helper function for Ig synthesis was found in MLN. Cells from none of the sites studied showed evidence of increased suppressor cell activity. These results show that MLN and LPL T cells in normal nonhuman primates differ from T cells in peripheral blood and spleen. While both MLN and LPL have a high proportion of T cells with the helper-inducer phenotype, cells with the suppressor-effector phenotype are infrequent in MLN, while cells with the suppressor-inducer phenotype are infrequent in LPL.