Antibody-dependent cellular cytotoxicity to virus-infected target cells: role of nylon wool-adherent T cells as effectors

This study was designed to elucidate whether populations of human blood lymphocytes other than non-T, non-B, Fc receptor-positive K cells can mediate antibody-dependent cellular cytotoxicity (ADCC) against target cells acutely infected with type 1 herpes simplex virus. With appropriate technical precautions, a subset of E rosette-positive, nylon wool-adherent T cells were found to be effective in killing antibody-coated target cells. Thus, there appears to be at least two relatively distinct populations of lymphocytes in human peripheral blood that function as effectors in ADCC: one that consists of E rosette-negative cells, the other of E rosette-positive cells. These findings suggest a possible relationship between “classical” E rosette-negative K cells and E rosette-positive T cells.     

Interactions between human lymphocytes and paramyxovirus-infected cells: adsorption and cytotoxicity.

The capacity of human lymphocytes to adhere to paramyxovirus-infected monolayers and their capacity to kill paramyxovirus-infected cells was investigated. A large fraction of human lymphocytes was found to adhere firmly to the paramyxovirus-infected monolayers. Predsorption of lymphocytes on mumps virus-infected cells impaired their adsorption to a second cell monolayer of the same type. The cytotoxic activity of lymphocytes against mumps virus-infected cells was also reduced after predsorption on mumps virus- or Newcastle disease virus-infected (NDV) cell monolayers. Exposure of lymphocytes to trypsin did not significantly decrease either adsorption or cytotoxicity. Pretreatment of lymphocytes with neuraminidase (NANase) partly inhibited adsorption whereas cytotoxicity was not decreased. Cell fractionation experiments after rosetting of the lymphocytes with sheep erythrocytes (E) indicated that T cells were equally or better adsorbed than "non-T" cells. Taken together with previous experiments which showed that the majority of T lymphocytes are not cytotoxic against mumps virus-infected cells these results suggest that adherence of lymphocytes to infected cells and cytotoxicity may be unrelated phenomena.     

Suppression of B cell responses by natural killer cells is mediated through direct effects on T cells

We examined the ability of human natural killer (NK) cells to modulate T cell-dependent mitogen-induced B cell responses. Highly purified NK cells inhibited the polyclonal antibody responses of autologous pokeweed mitogen (PWM)-stimulated unfractionated mononuclear cells in a reverse hemolytic plaque-forming cell (PFC) assay. Investigation of the possible mechanism(s) of the suppressor activity of NK cells revealed that lysis of mitogen-stimulated cells was unlikely. Chromium-51 release cytotoxicity assays of PWM-stimulated mononuclear cells did not demonstrate lysis by NK cells. Additionally, the monoclonal antibody 13.3, which abrogates NK cell cytolysis, did not reverse NK cell-dependent suppression of PFC formation. The putative lytic molecule elaborated by NK cells, NK cytotoxic factor, did not suppress B cell responses, further supporting a nonlytic inhibitory mechanism. That NK cell-derived lymphokines such as IFN-alpha, IFN-gamma, or IL-2 were uninvolved in the down-regulation of B cells was corroborated by the failure of antibodies to these mediators to reverse the suppression. NK cells did not suppress PFC formation when T cells were replaced by supernatants from PWM-stimulated T cells; additionally, NK cells had no effect on the generation of these necessary T cell factors. However, the coculture of T cells with NK cells resulted in the induction of suppressor activity within the T cell population suggesting that this was the mechanism of NK cell-mediated suppression of B cell responses.     

Regulation of T cell proliferation by cloned interferon-alpha mediated by Leu-11b-positive cells

The autologous T lymphocyte proliferative response (AMLR) induced by a B lymphocyte-enriched non-T, nonadherent cell population (NT, NAC) and by a macrophage-enriched population were both suppressed by the addition of a cloned interferon-alpha (IFN-alpha Con1) directly to the cultures. Preincubation of the stimulating NT, NAC with IFN-alpha Con1 resulted in comparable suppression. In contrast, preincubation of the macrophages with IFN-alpha Con1 resulted in significant augmentation of T cell proliferation. Depletion of Leu-11b-positive cells from the NT, NAC exposed to IFN-alpha Con1 restored the autologous T cell response. Addition of IFN-alpha Con1 activated Leu-11b-positive cells, isolated from the NT, NAC population, was suppressive of the AMLR. Although NK cytotoxicity was irradiation sensitive, suppression of the AMLR by IFN-alpha Con1-activated NT, NAC was resistant, suggesting that different subsets of cells or mechanisms by the same cells may have been responsible. These observations may offer insights into the potential role of cells with the NK phenotype, Leu-11b, and IFN in contributing to immuno-regulatory changes observed in clinical states associated with elevated concentrations of IFN.     

A Monoclonal Antibody Defining Human B Cell Differentiation Antigen (HLB-1 Antigen)

A new monoclonal antibody specific for human B cell differentiation antigen (HLB-1) is produced by a hybridoma established by fusion of splenocytes of mice immunized with the Epstein-Barr virus (EBV)-transformed peripheral B cell line, RPMI-8057. This monoclonal, antibody designated anti-HLB-1 monoclonal antibody (anti-HLB-1), reacted with surface immunoglobulin (sIg)-positive B cells of normal peripheral blood and lymphoid tissues and sIg-positive leukemic cells. The cells of T cell leukemia, non-T non-B acute lymphoblastic leukemia (ALL) and nonlymphoid leukemia were HLB-1 negative. These data were further confirmed by studying a panel of cultured human hematopoietic cell lines. Anti-HLB-1 reacted with B cell lines derived from pre-B, Burkitt's lymphoma, B cell type ALL and EBV-transformed peripheral B cells. Anti-HLB-1 was reactive with only one of three human myeloma cell lines, and with none of the T cell, myeloid and non-T non-B ALL cell lines. This newly defined HLB-1 antigen is different from other conventional human B cell markers such as sIg, Ia antigens, and receptors for the Fc portion of Ig and complement C3.     

Role of interferon-gamma in inducing cytotoxicity of peripheral blood mononuclear leukocytes to bovine herpesvirus type 1 (BHV-1)-infected cells

In the present study, the possible role of interferon (IFN)-gamma on the induction of cytotoxic activity of peripheral blood mononuclear leukocytes (PBML) from BHV-1-immune cattle was investigated. Supernatants obtained from BHV-1-immune PBML, stimulated under conditions similar to those required to demonstrate cytotoxicity, contained an antiviral substance capable of inducing 2'-5'-oligoadenylate synthetase activity in MDBK cells and MHC class II antigen expression on epithelial cells. These supernatants also contained IFN-alpha, but were devoid of tumor necrosis factor and interleukin-2 biological activities. Further studies during primary infection and hyperimmunization with BHV-1 showed that IFN-gamma production and non-MHC-restricted cytotoxicity against BHV-1-infected targets always occurred concomitantly, suggesting that they represent an important part of the detectable CMI responses mounted against this virus. Furthermore, it was also demonstrated that cytotoxicity of PBML against BHV-1-infected cells was reduced with the addition of antibodies to bovine IFN-gamma to the cytotoxic assay. Bovine recombinant IFN-gamma was able to enhance the in vitro cytotoxic activity of PBML from immune cattle, but not from their nonimmune counterparts. This suggests that other factors, in addition to IFN-gamma, may be essential in the development of non-MHC-restricted cytotoxic responses during BHV-1 infection.     

Establishment and characterization of a non-T, non-B cell lymphoma cell line with T cell receptor beta- and gamma-chain gene rearrangement and possessing MRK 20 monoclonal antibody-defined 85KD protein

A new non-T cell, non-B cell lymphoma cell line, designated IN-1, was established from the ascitic fluid of a patient with non-Hodgkin lymphoma. The IN -1 cells did not show any T cell and B cell immunophenotypes. There were rearrangements of T cell receptor beta- and gamma-chain gene, but no rearrangement of T cell receptor delta-chain gene and immunoglobulin JH gene. Electron microscopically, the cell had numerous pseudopods, mitochondria, vesicles, a conspicuous nucleolus, and scattered heterochromatin at the periphery of the nucleus. They reacted with only OKT9 monoclonal antibody. Molecular analysis revealed that cellular DNA from the IN-1 cells did not hybridize with Bam HI W fragment of EB virus DNA. Cytogenetic analysis showed that the chromosome number of the IN-1 was in the range of 61 -63 whose karyotype analysis demonstrated multiple numerical and structural chromosome changes. The IN-1 cells were resistant to etoposide in comparison with an IC50 of K562 (human chronic myelogenous leukemia). Interestingly, this IN-1 cell possessed 85 KD protein, but not P-glycoprotein, both of which are considered to be multidrug resistance-related proteins.     

Induction of interferon-gamma production by human natural killer cells stimulated by hydrogen peroxide

Interferon (IFN)-inducing activity of hydrogen peroxide in human peripheral mononuclear cells was investigated. Among the mononuclear cells, purified nonadherent cells produced IFN, but not B cells and monocytes. The maximal titer of IFN by purified nonadherent cells was observed after a 72-hr cultivation in the presence of 10(-2) mM H2O2 without affecting their viability. Furthermore, the purified nonadherent cells, but not the unpurified mononuclear cells, showed an augmented cytotoxicity to K562 when stimulated with hydrogen peroxide. By using Percoll discontinuous density gradient centrifugation, peripheral blood nonphagocytic and nonadherent mononuclear cells were divided into the low and high density fractions for which natural killer (NK) cells and T cells were enriched, respectively. The NK-enriched low density fractions, but not the T cell-enriched high density fractions, showed IFN production by the stimulation of hydrogen peroxide. IFN production as well as large granular lymphocytes and HNK-1+, Leu-11+ cells of the NK-enriched fractions were abrogated by treatment of the cells with monoclonal antibody against human NK cells (HNK-1+) but not against T cells (OKT3) in the presence of complement. Moreover, hydrogen peroxide-inducing IFN production seems to be regulated by monocytes. The antiserum neutralizing IFN-alpha and IFN-beta failed to neutralize substantially IFN-produced NK cells. The treatment with either pH 2 or antiserum-neutralizing human IFN-gamma resulted in marked reduction, indicating that a major part of IFN was IFN-gamma. The purified nonadherent cells showed IFN production and augmented cytotoxicity when cultured separately from activated macrophages by opsonized zymosan; furthermore, both IFN production and enhancement of cytotoxicity were abrogated by catalase. These results suggest that both exogenous and endogenous hydrogen peroxide might be responsible for a part of immunoregulation.     

Comparative analysis of the priming effect of human interferon-gamma, -alpha, and -beta on synergism with muramyl dipeptide analog for anti-tumor expression of human blood monocytes

Freshly isolated human peripheral blood monocytes from healthy volunteers were not cytotoxic to allogeneic A375 melanoma cells, but they were activated to the cytotoxic state by incubation in vitro with either des-methyl muramyl dipeptide (norMDP; minimal effective dose, 0.5 micrograms/ml) or recombinant human interferon-gamma (rIFN-gamma; minimal effective dose, 1 U/ml). A combination of subthreshold concentrations of these agents (norMDP, 0.5 micrograms/ml; rIFN-gamma, 10 U/ml) also induced significant cytotoxicity, indicating that the effects of norMDP and rIFN-gamma in monocyte activation are synergistic. Natural human IFN-gamma (nIFN-gamma) and norMDP also had similar synergistic effects. Pretreatment of rIFN-gamma with anti-IFN-gamma antibody completely inhibited its synergistic effect with norMDP in monocyte activation. Because pretreatment of rIFN-gamma and norMDP with polymyxin B did not interfere with their effects in monocyte activation, the preparations were not contaminated with lipopolysaccharide. Moreover, because pretreatment of monocyte monolayers with anti-Leu-11b antibody (anti-natural killer (NK) cell antibody) and complement did not interfere with the synergistic effects of norMDP and rIFN-gamma, whereas pretreatment with anti-Leu-M1 antibody (anti-monocyte antibody) caused complete inhibition of their effects, the observed tumor cytotoxicity of monocyte-rich monolayers was probably not due to a small number of adherent NK cells, but to the stimulation of the monocytes. Natural and recombinant IFN-alpha and IFN-beta at concentrations of greater than or equal to 100 U/ml also induced tumoricidal activity of monocytes, but unlike IFN-gamma, their effects were additive with norMDP, and they had less priming effect than IFN-gamma when they were added before norMDP to monocytes. These findings suggest that recombinant human IFN-gamma has much more synergistic potential with norMDP than IFN-alpha or IFN-beta, and this synergism of rIFN-gamma and norMDP for monocyte activation could be of clinical value in treatment of disseminated malignant diseases, because these compounds are readily available at standardized concentrations.     

Spontaneous production of gamma-interferon in cultures of T lymphocytes obtained from patients with Beh?et's disease

The spontaneous production of interferon (IFN) in the cultures of peripheral blood mononuclear leukocytes (PBML) obtained from 30 patients with Beh?et's disease was investigated. PBML obtained from each of 26 patients in the convalescent stage and four patients in the exacerbation stage were cultured at least twice without stimulation, and IFN activity in the culture fluid 2 to 7 days after the cultivation was assayed. Twenty PBML of normal healthy donors were also cultured simultaneously. PBML of all patients in the convalescent stage spontaneously produced high-titered IFN (60.0 +/- 9.5 IU/ml), but IFN activity produced in PBML cultures of four patients in the exacerbation stage was very low or was undetectable. Similarly, IFN was always detectable in the circulation of the patients whose PBML spontaneously produced IFN. All IFN activity detected both in the circulation and in the fluid of PBML culture from these patients was gamma-IFN, defined by virtue of its acid lability and antigenicity neutralized with antiserum for gamma-IFN and not with antisera for alpha- and beta-IFN. The cellular source of this gamma-IFN in the patients' PMBL was T lymphocytes and not non-T cells or macrophages. T lymphocytes did not require the help of macrophages. It is suggested that T lymphocytes of these patients may be stimulated by unknown causative agents in vivo and may produce gamma-IFN in vivo as well as in in vitro culture of T lymphocytes.     

Enhancement of a human antibody response in vitro mediated by interaction of interferon-alpha with T lymphocytes

This study describes the effects of human recombinant IFN-alpha 2 on antibody production in vitro. Whereas the inclusion of IFN-alpha 2 in cultures for 7 days had a relatively minor effect on pokeweed mitogen (PWM)-induced antibody production, it resulted in a dose-related enhancement of a hapten-specific primary antibody response. Comparison of PWM and IFN-induced [3H]thymidine uptake indicated that the observed IFN activation was not polyclonal. Pretreatment of T cells with IFN for 1 hr before recombination with untreated autologous B lymphocytes increased the anti-TNP response four-fold, whereas similar pretreatment of B lymphocytes had no effect. Furthermore, 2000 R x-irradiation of T cells before coculture with autologous B lymphocytes and IFN abrogated the TNP-specific response. These results indicate that IFN modulates TNP-specific antibody production via a radiosensitive T-helper function. Further subfractionation by panning suggests that the enhancement is mediated by the Leu-3a+ helper/inducer T cell subset. Evidence that a 1-hr exposure to IFN was sufficient to modulate antibody production prompted the examination of T cells for possible receptor mechanisms. Scatchard analysis of 125I-IFN-alpha 2 binding revealed approximately 65 high affinity IFN receptors per cell with an apparent dissociation constant (Kd) of 4.4 X 10(-10) M. This paper is the first demonstration of the role of T cells in mediating the effects of recombinant IFN-alpha 2 on human primary antibody responses in vitro. These data further suggest that the observed modulation of hapten-specific antibody production in vitro by IFN may involve the binding of IFN to specific cellular receptors expressed by T lymphocytes.     

Accelerated recovery of antigen-presenting cell activity by the administration of interleukin 1 alpha in 5-fluorouracil-treated mice

In this study, we investigated the effect of human recombinant interleukin-1 alpha (IL-1 alpha) on antigen-presenting cell (APC) activity of spleen cells in mice treated with 5-fluorouracil (5-FU). APC activity was determined by the antigen-specific proliferation of T cell clone D10.G4.1 cells. When mice were injected with 5-FU, APC activity of spleen cells was suppressed. The administration of IL-1 alpha accelerated the recovery from this suppression. The most accelerated recovery was observed when these mice were administered with IL-1 alpha both before and after the 5-FU treatment. The recovery was also accelerated when the mice were injected with IL-1 alpha after the 5-FU treatment, but not when injected before the 5-FU treatment. The injection of 5-FU also decreased the cell numbers of whole spleen cells, B cells, and non-T non-B cells (Ig- and Thy-1- cells). The administration of IL-1 alpha accelerated the recovery of the decreased cell numbers. Both B cells and non-T non-B cells possessed APC activity, but most APC activity of unseparated spleen cells was carried by non-T non-B cells. B cells possessed only 1/20 of the APC activity of non-T non-B cells. The injection of 5-FU decreased APC activity of both B cells and non-T non-B cells, but the administration of IL-1 alpha accelerated its recovery. Thus, the accelerated recovery of APC activity by IL-1 alpha was suggested to be due to the recovery in the numbers of APC activity-bearing cell subpopulations and also due to the recovery of the APC activity of each subpopulation. Possible mechanisms for the recovery were discussed.     

Virus-induced enhancement of lymphocyte-mediated antibody-dependent cytotoxicity (ADCC) in vitro

The effect of Parotis virus on antibody-dependent cellular cytotoxicity in vitro (ADCC) of human lymphocytes was investigated in a 51Cr-release assay and, at the effector cell level, in an ADCC plaque assay. Target cells were bovine or chicken erythrocytes, which are not susceptible to natural cytotoxicity (NK) of human lymphocytes. They were not killed when incubated with virus-treated lymphocytes in the absence of antibodies. Treatment of the lymphocytes or the target cells with small amounts of virus, however, resulted in a very significant enhancement of ADCC. The same results were obtained with live or UV-inactivated virus, suggesting that enhancement was a passive phenomenon not requiring infection. Enhancement was already significant after 3 hr of incubation, indicating that it was independent of endogenously released interferon. Enhancement of ADCC by virus was due to effector cell recruitment rather than due to the increase of the cytotoxic potential of the individual K cell. The highest frequency of effector cells was present in Percoll fractions enriched in large granular lymphocytes (LGL). Virus treatment resulted in recruitment of effector cells carrying T cell markers such as the T3 antigen (OKT3+), receptors for sheep erythrocytes, or Fc receptors for IgM. In contrast, the absolute number of K cells carrying the HNK-1 marker (Leu-7) or receptors for C3 fragments was not changed by the virus. It is concluded that Parotis virus enhances ADCC by improving effector cell-target cell contacts, resulting in recruitment of effector cells with T cell characteristics. Recruitment is accompanied by a significant reduction of the antibody concentration needed for ADCC induction. This virus-mediated enhancement of ADCC may be of importance for protection of the host in the early phases of a virus infection in which the amounts of anti-viral IgG antibodies capable of inducing cellular cytotoxicity may yet be very small.     

Increased sensitivity of cholera toxin B treated K562 cells to natural killer cells

Cholera toxin B-subunit (CTB) treatment of K562 erythroleukemia cells increased their sensitivity to be killed by NK-92 cells with more than 10%, compared to untreated cells. A similar treatment of non-T, non-B acute lymphoblastic REH leukemia cells, known to be unsensitive to NK cell mediated cytotoxicity, did not have any impact at all. Visualization of the cross-linked ganglioside_M1 (GM₁) using fluorescent labeled CTB, indicated accumulation of the fluorescence to one cap and a few smaller patches in both type of cells. Additional cross-linking using anti-CTB antibodies further accentuated capping and increased lysis in the case of K562 cells. Blocking experiments performed with anti-MICA/B, ULBP-2 and/or CD59 antibodies could not inhibit the increased sensitivity mediated by CTB.     

Suppressive effect of human natural killer cells on Epstein-Barr virus-induced immunoglobulin synthesis

The suppressive effect of human natural killer (NK) cells on Epstein-Barr virus (EBV)-induced immunoglobulin (Ig) synthesis by autologous B cells was investigated. By Percoll discontinuous density gradient centrifugation, low-density fractions enriched for NK cells were isolated from human peripheral blood lymphocytes. These NK-enriched fractions were added to purified autologous B cells in the presence of EBV, were cultivated for 8 days, and were examined for their suppressive effect on Ig synthesis by an enzyme-linked immunosorbent assay. The fractions markedly suppressed both IgM and IgG synthesis induced by EBV. It was possible to reduce the suppressive effect of NK-enriched cells by complement-dependent lysis of NK cells and Leu-11, but not by OKT3 monoclonal antibody, indicating that NK cells may be responsible for the suppression of Ig synthesis. Upon close examination of interferon (IFN) activity, it was revealed that the co-cultures of NK-enriched cells and EBV-infected B cells generated production of IFN-alpha, which might be produced by NK cells in response to EBV-stimulated B cells. Addition of anti-IFN-alpha but not anti-IFN-gamma serum almost completely abrogated the suppressive effect of NK-enriched cells on Ig synthesis, indicating that IFN-alpha produced are required for the NK cell-mediated suppression of Ig synthesis. However, addition of IFN-alpha into purified B cells showed no direct suppressive effect on EBV-induced Ig synthesis by B cells in the absence of NK cells. Nevertheless, NK cells when previously incubated with IFN-alpha and added to B cells showed a suppressor activity on Ig synthesis to a level higher than that of untreated NK controls. These results strongly suggest the possibility that NK cells display an interaction with EBV-infected B cells and produce IFN-alpha, which in turn activates NK cells. These activated NK cells suppress the Ig synthesis by B cells, which undergo transformation induced by EBV.     

Systemic administration of human leukocyte interferon to melanoma patients. III. Increased helper:suppressor cell ratios in melanoma patients during interferon treatment

Malignant melanoma patients treated with human leukocyte interferon (IFN-alpha) displayed increased natural killer (NK) cytotoxicity to K562 targets within the first 2 weeks of therapy. This study explored the possibility of T-cell regulation of this NK response, as evidenced by a variation in T-cell subpopulations. T-cell subset levels were studied in 9 patients who received daily doses of IFN-alpha over a period of 42 days. Five monoclonal antibodies to T-cell surface markers were used: Leu 1 (pan-T), Leu 2a (T suppressor/cytotoxic), Leu 3a (T helper/inducer), HNK-1 (Leu 7, a marker for NK cells), and B73.1 (an antibody against the Fc receptor on NK/K cells). Percentages of these markers were measured on days 0, 3, 7, and 21 of treatment. Percentages of Leu 1-positive cells and Fc-receptor-positive cells remained relatively constant throughout treatment in all patients. A trend toward a decrease in suppressor cells and an increase in helper cells peaking on day 7 and returning to earlier values by day 21 was found in 5 patients. The increase in NK cytotoxicity was not reflected consistently in proportions of HNK-1-positive cells or Fc receptor-bearing cells within the first week of therapy. The most significant finding was an increase in the helper:suppressor cell ratio peaking on day 7 and returning to pretreatment values by day 21. This increase was seen in every patient studied. The average pretreatment Leu 3a:Leu 2a ratio was 0.67 increasing to an average value of 1.47 on day 7 (p less than 0.005). Leu 3a:Leu 2a ratios returned to pretreatment values, in parallel to NK activity, despite continuation of interferon therapy.     

Natural killer-like function of activated T lymphocytes: differential blocking effects of monoclonal antibodies specific for a 90-kDa clonotypic structure

A monoclonal antibody termed anti-NKTb has been generated following immunization of mice with cloned human cells (JT9) displaying natural killer (NK)-like activity. This antibody has the capacity to block cytotoxicity of the immunizing clone against several targets. In the present study, anti-NKTb was compared with a monoclonal antibody termed anti-NKTa that had previously been generated against JT9 cells and that had also been shown to block the NK-like function of these cells. The expression of a NKTb determinant, like that of NKTa, was found to be restricted to two NK active clones derived from the same individual, JT9 and JT10, both of which have the same mature T-cell phenotype (T3+, T8+, T11+). Comodulation, immunoprecipitation, and competitive binding experiments showed that both antibodies are directed to the same 90-kDa heterodimer associated with the T3 structure on the cell surface. However, cytotoxicity blocking studies suggested that NKTa and NKTb may represent functionally distinct epitopes of this 90-kDa molecule. Anti-NKTa uniformly blocked the cytotoxicity of both JT9 and JT10 cells when tested against 11 randomly selected target cell lines. In contrast, anti-NKTb totally blocked the cytotoxicity of these cloned cells against some targets (i.e., HPB-ALL, Nalm-1) but had very little effect when cytotoxicity was measured against other target cells (i.e., K562, U937, KG-1). This selective blocking effect, therefore, supports the notion that the heterodimer defined by the NKT antibodies is involved in the process of target cell recognition rather than in the cytolytic pathway of the cloned effector cells. Moreover, the unique functional effects of anti-NKTb suggest that additional levels of complexity exist in the specific recognition mechanisms of these clonal populations of NK active mature T lymphocytes.     

Production of B cell growth factor by a Leu-7+, OKM1+ non-T cell with the features of large granular lymphocytes (LGL)

The present study reports the characterization of a non-T cell from human peripheral blood which is capable of releasing BCGF. This BCGF-producing non-T cell had a T3-, T8-, Leu-7+, OKM1+, HLA-DR-, Leu-11- surface phenotype and was likely to belong to the so-called large granular lymphocyte (LGL) subset because: after fractionation of non-T cells according to the expression of Leu-7 or HLA-DR markers, it was found in the Leu-7+, HLA-DR- fractions that were particularly enriched in LGL; it co-purified with LGL on Percoll density gradients; and it expressed Leu-7 and OKM1 markers that are shared by a large fraction of LGL. Although co-purified with cells with potent NK capacities, the BCGF-producing cell was not cytotoxic, because treatment of Leu-7+ cells with Leu-11 monoclonal antibody and complement abolished the NK activity but left the BCGF activity unaltered. The factor released by this LGL subset was not IL 1 or IL 2 mistakenly interpreted as BCGF, because: a) cell supernatants particularly rich in BCGF activity contained very little or no IL 1 or IL 2; b) BCGF-induced B cell proliferation was not inhibitable by anti-Tac antibodies (this in spite of the expression of IL 2 receptor by a proportion of activated B cells); and c) BCGF activity was absorbed by B but not T blasts.