Accessory cell function of human alveolar macrophages in antigen-induced T lymphocyte proliferation

We compared the accessory cell function of human alveolar macrophages (AM) to that of human blood monocytes (Mo) obtained by bronchoalveolar lavage and venipuncture from normal volunteers. Graded numbers of either AM or Mo were added to autologous peripheral blood T lymphocytes that were stimulated with a purified protein derivative of tuberculin (PPD). Either AM or Mo were cocultured with allogeneic T lymphocytes in mixed lymphocyte reaction (MLR) experiments. Both AM and Mo supported the PPD-induced T lymphocyte proliferation and allogeneic MLR at low ratios of AM or Mo to T lymphocytes with similar efficiency. However, AM showed marked suppressive effects at higher ratios of AM to T lymphocytes (1:1). PPD-pulsed AM, but not AM killed by physical treatments (heat, freeze-thaw, sonication), induced T lymphocyte proliferation. An indirect immunofluorescent study demonstrated that most AM express HLA-DR antigens. Furthermore, AM synthesized DR antigens with molecular weights of 33,000 and 29,000-31,000 daltons. When AM were treated with both anti-DR monoclonal antibody and complement, PPD-induced T lymphocyte proliferation and MLR were diminished. These results suggest that human AM function as accessory cells in the antigen-induced T lymphocyte proliferation and DR antigens on AM play an important role in the accessory cell function.     

Loss of allogeneic T-cell activating ability and Langerhans cell markers in human epidermal cell cultures

Human Langerhans cells are the only epidermal cells that express the T6 and HLA-DR antigens and are responsible for the in vitro allogeneic T-cell proliferative responses in the mixed skin cell lymphocyte reaction (MSLR). To investigate the presence of Langerhans cells in normal human epidermal cell cultures, epidermal cell suspensions obtained from normal human skin specimens and from the subsequent epidermal cell cultures were analyzed by indirect immunofluorescence for the presence of T6 and HLA-DR determinants. In parallel, MSLRs were conducted with suspensions of cultured epidermal cells as stimulatory cells. These studies present evidence that when human epidermal cells are grown in culture, they loose both the ability to stimulate the proliferation of allogeneic T lymphocytes in vitro and their expression of HLA-DR and T6 antigens. The T6 antigens were lost during the first 2 weeks of culture, while HLA-DR determinants were still expressed by a small number of cells and were progressively lost through duration of cultures. The loss of HLA-DR antigens closely paralleled the progressive inability of human epidermal cells in culture to stimulate allogenic T cells in MSLR.     

Heated lymphocytes express HLA-DR antigens despite their inability to stimulate in MLC

We have utilized serological techniques and mixed lymphocyte culture (MLC) reactions to examine HLA-DR and HLA-D expression by heated (45 degrees C for 1 h) lymphocytes in order to study the functional relationship of these antigens. Heated lymphocytes do not stimulate proliferation of allogeneic lymphocytes in MLC, yet they express HLA-DR antigens. The fraction of peripheral blood lymphocytes (PBL) expressing DR is not altered by heating, nor is the staining intensity altered as detected by fluorescence microscopy. Alloantisera to "B cell alloantigens" recognize HLA-DR determinants on heated cells without any detectable change in either specificity or quantitative cytotoxic effects. Flow cytometry with monoclonal antibody demonstrates only minimal decrease in HLA-DR expression after heating. Thus stimulation in MLC requires more of the stimulating cell than the mere expression of HLA-DR.     

Monoclonal antibodies against HLA-DR antigens acting on stimulator cells prevent OKT8+ T lymphocytes from acquiring sensitivity to interleukin 2 and expressing suppressor function

Purified OKT8⁺ but not OKT4⁺ T lymphocytes generated suppressor activity in autologous mixed lymphocyte reactions (AMLR) in the presence but not in the absence of interleukin 2 (IL 2) as determined in proliferative responses of peripheral blood mononuclear cells induced by Concanavalin A, the OKT3 monoclonal antibody and allogeneic cells (indicator systems for suppressor activity used in this study). Furthermore, treatment of AMLR-activated T cells with the OKT8 antibody plus complement abolished suppressor cell activity whereas treatment of the cells with the OKT4 antibody plus complement did not. The three monoclonal anti-HLA-DR antibodies used in this study abrogated the induction, but not the effector phase, of suppressor cells in AMLR. The anti-DR antibodies acted specifically on the stimulator non-T cells and not on the responder T cells. The addition of IL2 to AMLR cultures performed in the presence of the anti-DR antibodies did not restore or increase the suppressor activity whereas IL2 added to AMLR cultures exposed to control antibodies or medium alone increased the suppressor activity. Moreover, purified OKT8⁺ T cells cocultured with autologous non-T cells and IL2, in the presence of the anti-DR antibodies, neither responded to IL2 by proliferating nor expressed suppressor function. In contrast, OKT8⁺ T cells from similar cultures, but performed in the absence of the anti-DR antibodies or exposed to control antibodies, proliferated to IL2 stimulation and exhibited suppressor activity. Unactivated OKT8⁺ T cells were unresponsive to IL2 and unable to express suppressor function. Finally, the addition of the OKT8 antibody (in the absence of complement) to AMLR cultures had no effect on the generation of suppressor cells. From these results, we conclude the following: (a) OKT8⁺ T lymphocytes become sensitive to IL2 by interacting with HLA-DR antigens on the stimulator non-T cells and, with the help of IL2, they express suppressor cell activity; (b) the OKT8 antigenic determinant on AMLR-activated suppressor cells does not seem to participate in their process of activation; (c) results of previous studies showing that OKT4⁺ T lymphocytes become sensitive to IL1 and are capable of synthesizing IL2 after interaction with HLA-DR on the stimulator cells, and the findings presented here, lead us to suggest that both OKT4⁺ and OKT8⁺ T lymphocytes possess receptors for self HLA-DR antigens and that neither the OKT8 nor the OKT4 antigenic determinants on these cells are involved in the recognition of HLA-DR antigens. The suppressor activity generated in AMLR may be one mechanism whereby effector self-tolerance is maintained in the face of inductive self-recognition.     

Strong lymphoproliferative suppressive function of PLT clones specific for SB-like antigens

From a total of 37 different priming combinations between donors matched for HLA-A,B, and/or Dw/DR, but mismatched for SB, antigens, T cell clones strongly restimulated with concordance for SB specificities were isolated from only two. Most of the alloproliferative (PLT) clones obtained were restimulated by determinants not correlated with any currently known HLA product. Nonetheless, their stimulation was inhibited by a monoclonal antibody TU 39, which preferentially blocks stimulation by SB-, rather than by Dw/DR-associated determinants. Despite having an OKT4+, OKT-, Leu8- phenotype, and secreting Interleukin-2 after contact with stimulatory cells, these clones strongly suppressed proliferative responses of cloned PLT reagents as well as unprimed lymphocytes in mixed leukocyte cultures. They may thus represent a novel type of immunoregulatory T cell, stimulated by SB-related antigens, which despite their "helper/inducer" phenotype are able directly to suppress lymphoproliferative responses.     

T-Cell Proliferation and Expression of MHC Class II Antigens

Two monoclonal antibodies to major histocompatibility complex (MHC) class II antigens, which in combination identify β chains encoded by the SB and DR loci, were used to investigate which of these gene- products were expressed at the cell surface of unstimulated T cells and at various stages of mitogen-induced T-cell maturation. In tests on blood lymphocytes from healthy donors 12% of Tcells expressed class II antigens, but only SB antigens were expressed. During activation of T lymphocytes, SB-coded antigens were expressed before DR antigens, and the kinetics of SB expression correlated with the proliferative response of T cells. These results and consideration of recent reports from other laboratories lead us to suggest that 58-coded class II antigens play a role in T-cell proliferation.     

Heterogeneity of human T-lymphocyte clones generated from autologous mixed-lymphocyte cultures

To assess the heterogeneity of T cells activated during the autologous mixed-lymphocyte reaction (AMLR), a cloning procedure based on the soft agar colony assay was developed. Supernatants of allogeneic MLR cultures were used as a source of interleukin 2 (IL-2) to generate two types of colonies: upper and lower colonies. Both types of colonies were expanded in long-term cultures using supernatants of phytohemagglutinin (PHA)-activated lymphocyte cultures. Cloned cells underwent secondary proliferation when stimulated by autologous monocytes, although certain clones also responded to autologous B cells. Most autoactivated clones expressed the serological determinants of HLA-DR, MB, and MT and were OKT3+, OKT4+, OKT8-. They did not induce cytolysis of autologous monocytes, B lymphoblasts, or PHA blasts nor did they express natural killer-like activity toward K562 cells. Several autoactivated clones (irradiated with 500 R) expressed helper activity, shown by an enhancing effect on AMLR proliferation. Furthermore, many irradiated clones were capable of inducing proliferation of autologous T cells in the absence of accessory cells. These observations suggest that autoactivated clones generated from soft agar colonies may interact with autologous T lymphocytes.     

Homogeneity of HLA-DQ,DR phenotypes in lymphocyte subsets of normal individuals

The study was performed to evaluate the association of HLA-DQ and DR antigens with the composition of peripheral blood lymphocytes. B cells, T cells, and T subsets were enumerated in 200 normal individuals by indirect immunofluorescence microscopy using the monoclonal antibodies OKT3, OKT4, OKT8, and OKIa1. Results were related to the HLA-DQ,DR phenotypes of the investigated population. No significant correlation between any of the lymphocyte subsets and of the HLA-DQ,DR antigens was found.     

Function of alloproliferative T lymphocyte clones correlates better with their class II recognitive specificity than with their cell surface phenotype

Alloproliferative primed lymphocyte typing (PLT) clones recognizing determinants associated with HLA-DR/Dw, SB, MB, or novel "SB-like" gene products were screened for their ability to suppress lymphoproliferative responses in primary and secondary mixed lymphocyte cultures (MLC), and for their surface marker phenotypes. Two nonsuppressive HLA-D specific PLT clones were OKT4-, OKT8+ whereas all others possessed an OKT4+, OKT8-, Leu-8- phenotype. All clones secreted interleukin 2 (IL2) after specific stimulation. The eight PLT clones specific for "SB-like" antigens strongly suppressed MLC, whereas only one of 35 DR/Dw-specific, and none of 20 SB-specific PLT clones did so. Suppressive activity of such PLT clones was not restricted by major histocompatibility complex products, was radioresistant (20 Gy), and was not caused by absorption of IL2 or by cytotoxicity of the cloned cells. Suppressive clones exerted their effects directly on proliferating T cells, as assessed by their ability to prevent growth of cloned PLT cells stimulated by B cell lines, and their ability to block primary MLC even when added 96 h after the start of the 144-h culture. Culture supernatants from suppressive, but not from nonsuppressive, PLT clones also strongly and nonspecifically inhibited lymphoproliferative responses. The suppressive factor(s) was not dialyzable, not sensitive to pH 2 or heat treatment and not cytotoxic. Thus, all T cell clones proliferating against novel "SB-like" but not SB antigens, as well as rare clones specific for D region determinants, possess powerful nonspecific suppressive activities dissociated from their "helper-related" OKT4+, OKT8-, Leu 8-, IL2-secreting phenotypes.     

OKT4+ T cell abnormality in patients with active systemic lupus erythematosus: HLA-DR antigen expressions

The objective of this study was to define immunologic T cell abnormality characteristic of active systemic lupus erythematosus (SLE). Eight of nine patients who had severe clinical and laboratory manifestations of active SLE had a characteristically marked increase in OKT4+ and a decrease in OKT8+ T cells. Using OKIa1 and OKDR monoclonal antibody, we found that, in circulating blood of all patients with active SLE, an increased percentage of Ia+ and DR+ T cells is present compared to inactive SLE. Five of these active SLE patients had Tac+ antigens, an interleukin 2 receptor on OKT4+ and OKT8+ T cell subsets in resting blood. The present study demonstrates that Ia+ and DR+ antigens are selectively expressed on the majority of OKT4+ T cell subsets of all patients with active SLE, whereas Ia+ and DR+ antigens are expressed almost equally on both OKT4+ and OKT8+ T cell subsets in inactive SLE. The elevated percentage of Ia+, DR+, OKT4+ T cells in active SLE was accompanied by a highly depressed proliferative response to T cell mitogens, phytohemagglutinin and concanavalin A. However, OKT8+ T cell subsets in active SLE possessed a normal proliferative response to these T cell mitogens. We conclude that this abnormality of activated OKT4+ T cells bearing HLA-DR antigens may play a role in the development of active SLE.     

Hepatic vascular endothelial cells heterogenously express surface antigens associated with monocytes,macrophages and T lymphocytes

Summary During studies of the antigenic and functional properties of hepatic sinusoidal lining cells in situ, we found that only the sinusoidal endothelial cells share antigens with a peripheral blood macrophage subset capable of presenting soluble antigens and triggering autologous mixed lymphocyte reactions. They were HLA-DR+, OKM1–, OKM5+. Vascular endothelial cells in the portal areas and central veins were HLA-DR+, OKM1– and OKM5–. The sinusoidal endothelial cells also expressed an antigen found on helper/inducer (OKT4 and Leu3 a) T lymphocytes. Thus, the present study suggests that endothelial cells in different anatomic compartments in the liver heterogenously express surface antigens associated with monocytes, macrophages and T lymphocytes and possess distinct immunological functions.     

An immunohistological analysis of lymphocyte subpopulations and their microenvironment in the synovial membranes of patients with rheumatoid arthritis using monoclonal antibodies.

We have used monoclonal antibodies of the orthoclone (OKT) series to identify T cell subsets in an immunohistological analysis of the synovial membranes obtained from normal individuals and patients with osteoarthritis or rheumatoid arthritis. T cells of the inducer and the suppressor/cytotoxic subsets were identified by the OKT4 and OKT8 antibodies respectively while HLA-DR (Ia-like) antigens were recognized by a conventional antiserum. In the normal and osteoarthritic synovial membranes, virtually no lymphocytes were identified whereas the mononuclear cell infiltrates of the rheumatoid synovial membranes were composed predominantly of T cells expressing the OKT4 inducer phenotype with few OKT8+ suppressor/cytotoxic cells. The OKT4+ cells were found to be intimately related to B cells and strongly HLA-DR+ cells which morphologically resembled the interdigitating cells of lymph nodes. The micro-anatomical arrangement of these different cell types in the mononuclear infiltrates of the rheumatoid synovial membranes closely resembled that of the paracortical or T cell dependent area of normal lymph nodes except few OKT8+ lymphocytes were present. These findings are explained in terms of rheumatoid arthritis as a disease of altered T lymphocyte/macrophage immunoregulation.     

Functional characteristics and differential expression of class II DR,DS, and SB antigens on human melanoma cell lines

Although most cultured melanoma cell lines express DR Class II molecules, many of these do not also express the DS (MB) Class II molecules as detected by a monoclonal antibody specific for DS. Cells lacking either DR or DS molecules or both could only be induced to express DR antigens in rare cases by combined incubations with azacytidine and Interleukin-2 conditioned medium, although the expression of DR molecules on fibroblasts or U937 monocytes could more easily be induced under the same culture conditions. Melanoma cells expressing DR antigens could function in antigen presentation for the histocompatibility antigens themselves and for DR specific presentation of TNP determinants to allogeneic T-cells sensitized to TNP modified lymphocytes and showing restriction in their responses to the specificity of the DR molecules expressed on the original, autologous senzitizing cells. DR positive melanoma cells could not, however, be demonstrated to function in the presentation of any of the soluble antigens tested. All DR positive melanoma cells also expressed SB antigens, but these were not detected on DR negative melanoma cells. These studies collectively indicate that the expression of Class II histocompatibility antigens on diverse cell types is subject to differential regulatory control and is associated with differences in their functional activities.     

Lymphocyte Subsets and Activation Antigens in a Reference Population: A Flow Cytometric Study Using Single and Double Antibody Staining

The transferrin receptor (TR), the HLA DR antigen (DR), and the antigen binding OKT10 (T10) are present on activated lymphocyte populations. The authors have studied their expression and that of antigens defined by eight commercial monoclonal antibodies on peripheral blood lymphocytes of 50 healthy hospital workers aged 23–60 years. A whole blood lysis technique was employed and cells were enumerated on a flow cytometer. The percentage of cells bearing the three activation antigens were generally low: mean values for T10 being 7.2%; for TR 1.8%; and for DR 8.8%. There was, however, considerable variability, with occasional subjects having 20% or more cells positive for one of the three antigens. High values of one activation antigen did not correspond with high values of another in the same subject. Nor was there correlation of the presence of activation antigens with the occurrence of cells bearing T11, T4, T8, Leu 1, Leu 2a, Leu 3a, or Leu 7. Double labelling with the following pairs of fluorescein (FITC) and phycoerythrin (PE) labeled antibodies: Leu 2a, DR; Leu 3a, DR; Leu 3a, Leu 2a; TR, DR, indicated that simultaneous expression of the corresponding antigens do not normally occur on lymphocytes of healthy individuals. Double labelling with B1 and DR in five subjects indicated the presence of B1 (+) DR (-) cell population. No pattern of relationship could be detected among common clinical variables or HLA type and an increased expression of activation antigens.     

Characterization and expression of the HLA-DC antigens defined by anti-Leu 10

The expression of HLA-DC antigens on peripheral blood mononuclear cells, in tonsil and lymph node tissue sections, on tumor cell lines, and on activated T cells was studied using monoclonal antibody, anti-Leu 10. Anti-Leu 10 reacts with HLA-DC molecules on homozygous B cell lines expressing HLA-DR 1,2,4,5,6,8, and 9. It reacts with heterozygous B lymphocytes expressing DR7 and DRw10, suggesting it also recognizes HLA-DC molecules linked to DRw10. The HLA-DC molecules detected by anti-Leu 10 are expressed on all Ig-positive and DR-positive peripheral B lymphocytes and an apparent subpopulation of DR-positive periperal blood monocytes. Two-color immunofluorescence experiments using phycoerythrin-anti-HLA-DR (L243) and FITC-anti-Leu 10 demonstrated a correlation of the amounts of HLA-DR and DC antigens expressed on B lymphocytes. Cells expressing relatively low or high amounts of one Class II molecule express respectively low or high amounts of the other Class II molecule. Anti-Leu 10 reacted with all B lymphocyte derived tumor cell lines not with lines of myeloid or erythroid origin, and with only one T cell derived line, HUT-78 which has an activated T cell phenotype. Consistent with this result, anti-Leu 10 binding suggested the presence of HLA-DC on activated T cells in lymphoid tissue, in addition to staining B cells. HLA-DC was also detected on mitogen and MLC activated T cells by anti-Leu 10 binding. Anti-Leu 10 is, therefore, a useful reagent for further studies of the role of HLA-DC in T cell activation and in normal B cell and monocyte functions.     

Lymphocyte subsets and activation antigens in a reference population: a flow cytometric study using single and double antibody staining

The transferrin receptor (TR), the HLA DR antigen (DR), and the antigen binding OKT10 (T10) are present on activated lymphocyte populations. The authors have studied their expression and that of antigens defined by eight commercial monoclonal antibodies on peripheral blood lymphocytes of 50 healthy hospital workers aged 23-60 years. A whole blood lysis technique was employed and cells were enumerated on a flow cytometer. The percentage of cells bearing the three activation antigens were generally low: mean values for T10 being 7.2%; for TR 1.8%; and for DR 8.8%. There was, however, considerable variability, with occasional subjects having 20% or more cells positive for one of the three antigens. High values of one activation antigen did not correspond with high values of another in the same subject. Nor was there correlation of the presence of activation antigens with the occurrence of cells bearing T11, T4, T8, Leu 1, Leu 2a, Leu 3a, or Leu 7. Double labelling with the following pairs of fluorescein (FITC) and phycoerythrin (PE) labeled antibodies: Leu 2a, DR; Leu 3a, DR; Leu 3a, Leu 2a; TR, DR, indicated that simultaneous expression of the corresponding antigens do not normally occur on lymphocytes of healthy individuals. Double labelling with B1 and DR in five subjects indicated the presence of B1 (+) DR (-) cell population. No pattern of relationship could be detected among common clinical variables or HLA type and an increased expression of activation antigens.     

Genetically Appropriate Expression of HLA and DR (IA) Alloantigens on Human Melanoma Cell Lines

Studies of the expression of HLA and DR alloantigens on cultured human melanoma cells in comparison with those expressed on peripheral lymphocytes and B-cells derived from the same patients have shown that the HLA-A,B, and C locus antigens expressed on the cultured tumor cells were consistent with those expected from the typing of peripheral blood lymphocytes. One melanoma cell line failed to express all the HLA antigens expected from donor typing. All five of the lines tested also expressed DR antigens and in three instances these could be demonstrated to have genetically consistent allotypes. However, in preliminary studies stimulation of allogeneic lymphocytes by the DR positive melanoma cells could not be demonstrated.     

Human thymic epithelial cells express functional HLA-DP molecules

HLA-DP molecules function as restriction elements in the presentation of foreign antigens to T cells by antigen presenting cells and certain HLA-DP molecules confer susceptibility to autoimmune disease. Because HLA molecules play an essential role in thymic selection and elimination of autoreactive T lymphocytes, we examined whether human thymic epithelial cells (TEC) expressed HLA-DP molecules. We present evidence that TEC obtained from short time culture express low but significant levels of HLA-DP molecules. The expression of HLA-DP molecules was comparable to or higher than the expression of HLA-DQ but lower than that of HLA-DR. Upon IFN-γ treatment, HLA-DP expression was strongly upregulated. Since HLA-DQ and DR expression was upregulated in parallel, the hierarchy between MHC class II isotypes remained unchanged following interferon treatment. TEC elicited significant proliferation of HLA-DP allospecific primed lymphocyte typing (PLT) CD4 T cell lines. IFN-γ treatment strongly upregulated the HLA-DP allospecific PLT responses whereas other PLT responses remained largely unchanged. In conclusion, these data indicate that human thymus epithelial cells express significant levels of functional HLA-DP molecules.     

T-cell subsets in human lymphocytes maintained in IL-2 medium after PHA or mixed lymphocyte reaction activation

The culture of human T lymphocytes in interleukin-2 (IL-2) containing growth factor medium results in a significant shift in the T-lymphocytes subsets isolated from such cultures at weekly intervals. If normal peripheral blood mononuclear cells are stimulated with phytohemagglutinin (PHA) or in a mixed lymphocyte reaction (MLR), the resulting T lymphoblasts can be propagated in growth factor medium. Staining of the cultured cells with monoclonal antibodies was evaluated by indirect immunofluorescence on a laser-activated flow cytometer (Ortho Spectrum III). The antibodies used were: OKT3 (mature T lymphocytes), OKT4 (helper/inducer T lymphocytes), OKT8 (cytotoxic/suppressor T lymphocytes, OKT10 (immature and "activated" lymphocytes), OKT11a (cells which rosette with sheep erythrocytes), and OKIa-I (HLA-DR constant region). Both PHA and MLR activation resulted in initial preservation of the OKT4+ subset predominance over OKT8+ T lymphocytes noted on normal circulating blood lymphocytes. However, during culture in T-cell growth factor medium, there was a progressive increase in the percentage of OKT8+ cells, and a concomitant decrease in OKT4+ lymphoblasts. The increase in OKT8+ cells in the MLR-stimulated cultures was paralleled by an increase in specific cell-mediated cytotoxicity against the stimulating lymphocyte population. In addition to the shift in T-lymphocyte subset, there was virtual 100% staining with OKT3 and OKT11a, indicating the T-cell nature of the proliferating cells. OKT10 which was present on a small subset of fresh blood lymphocytes appeared rapidly in stimulated cultures, and was retained on virtually all lymphoblasts of either OKT4+ or OKT8+ subset. OKIa-1 cells increased slowly in PHA-stimulated cultures. HLA-DR+ T cells were detected earlier in MLR cultures. The activation of T lymphocytes results in a significant increase in the number of molecules of OKT11a bound per cell, in concert with the increased avidity of T lymphoblasts for sheep erythrocytes. The significant change in the phenotype and function of lymphoblasts isolated from long-term cultures demonstrates the importance of monitoring cultures, and the potential hazards in equating a cultured cell population with a freshly isolated one.     

A clonal analysis of human peripheral blood lymphocytes displaying natural killer-like activity

Human Fc gamma receptor-bearing lymphocytes and T cells, prepared by sorting peripheral blood lymphocytes using the B73.1 monoclonal antibody, have been cloned by limiting dilution. Although quiescent lymphocytes of either cell type were unresponsive to interleukin 2 (IL 2), following induction with phytohemagglutinin and/or the BSM B lymphoblastoid cell line they could be expanded in IL 2 utilizing a mixed irradiated feeder system. Clones originating from B73.1+ lymphocytes displayed a characteristic large granular lymphocyte (LGL) morphology but were otherwise functionally and phenotypically heterogeneous. Of 36 clones analyzed 19 displayed significant natural killer (NK)-like activity, each clone having a target cell repertoire identical to uncloned NK effectors. Furthermore, only a minority of clones (i.e. 5) displayed significant antibody-dependent cellular cytotoxicity, while levels of lectin-induced cellular cytotoxicity were normally commensurate with a clones level of NK-like activity. No correlation was evident between the phenotype of a clone and its cytotoxic activity since of 12 cytotoxic clones phenotyped, 8 expressed the OKT3 antigen but lacked the B73.1 antigen; 2 lacked the OKT3 antigen but expressed the B73.1 antigen and one lacked both OKT3 and B73.1 antigens. In addition the expression of OKT8 and OKT4 antigens was not in any way predictive of the cytotoxic capacity of a given clone. Several clones expressing T cell associated antigens bore a phenotype that distinguished them from T cell clones insofar as T cell subset antigens were expressed in the absence of the OKT3 antigen and vice versa.(ABSTRACT TRUNCATED AT 250 WORDS)