Activation through CD3 molecule leads to clonal expansion of all human peripheral blood T lymphocytes: functional analysis of clonally expanded cells

Monoclonal antibodies directed against CD3, a T cell-specific surface molecule essentially required for activation of these cells, are highly mitogenic for resting human peripheral blood T lymphocytes. A predetermined optimal concentration of anti-CD3 monoclonal antibody WT32 was employed to activate T cells cultured in limiting-dilution microcultures containing irradiated feeder cells and exogeneous interleukin 2. Frequencies of cells triggered into clonal expansion by WT32 under these culture conditions were 0.57 to 0.72 and 0.90 to 1.10 in peripheral blood mononuclear cells and E rosette-positive cells, respectively. It appeared that WT32 could induce virtually every human peripheral blood T lymphocyte to expand into a clonal progeny of 5 to 40 X 10(4) cells in 14 to 18 days of culture. This progeny was tested for cytolytic effector function with 51Cr-labeled murine P815 targets in the presence of PHA to detect all cytotoxic T lymphocytes (CTL) regardless of specificity, and was also assayed for natural killer like activity against K562 target cells. Frequencies of cells in the human peripheral blood T cell compartment giving rise to a clonal progeny expressing CTL function was 1/3, whereas 1/6 to 1/5 expanded into effector cell populations possessing NK activity. Frequency analysis of CD4-positive and CD8-positive populations, activated by WT32 in limiting dilution microcultures, demonstrated that 1 to 6% of the CD4-positive and 100% of the CD8-positive peripheral blood T lymphocytes expanded into CTL.     

Functional and morphologic characterization of human T cells continuously grown in vitro.

Long-term growth (now over 13 months) of thymus-derived lymphocytes from numerous normal human bone marrow and peripheral blood cell samples was accomplished by using a factor present in media obtained from mitogen-stimulated human peripheral blood lymphocytes. This long-term growth could neither be initiated nor maintained by mitogens alone. All cell cultures were greater than 90% E rosette-positive, whereas the tests for B cell markers, surface IgG and IgM, and EAC rosette were routinely negative. There was no evidence for the presence of granulocytes, monocytes, and their precursors in these cultures. The E rosette-positive cells were then tested to see if they had T cell functions. PHA, Con A, and pokeweed mitogens stimulated lymphproliferative responses in these cultures comparable to those of fresh peripheral blood cells. These proliferating cells were also able to release cell mediators, such as interferon and colony-stimulating activity. Further evidence for the T lymphocyte nature of these cultured cells was obtained from one-way mixed leukocyte cultures in which these cells responded to but were unable to stimulate allogeneic cells. The functional and morphologic characteristics of these cultured cells show that these cells are T cells that grow continuously in vitro.     

Human killer cells and natural killer cells: distinct subpopulations of Fc receptor-bearing lymphocytes

Unstimulated human peripheral blood lymphocytes were depleted of K cells, which mediate antibody-dependent cellular cytotoxicity (ADCC) without removing NK cells, which mediate natural killing (NK). K cell depletion was achieved by buoyant centrifugation removal of lymphocytes that bound to glutaraldehyde-treated P815-AB cells at high lymphocyte-to-target ratios. Likewise, NK cells were removed with glutaraldehyde-treated K562 cells without removing K cells. Furthermore, both cytotoxic cell populations were observed directly in one agarose single-cell cytotoxic assay (ASCA) using P815-AB and K562 cells simultaneously as target cells. Moreover, the percentage of total cytotoxic cells was equal to the sum of the percentage of K and NK cells observed in separate ASCA. Collectively, these results indicate that K cells and NK cells are distinct subsets of FcR-bearing lymphocytes. One subset, K cells, has more avid Fc receptors (fcR) than NK cells and are 'activated' via thier FcR to kill antibody-coated target cells. The second subset, NK cells, have less avid FcR and are not 'activated' through their FcR to kill antibody-coated target cells.     

Low affinity E-rosette formation by the human K cell.

Human T lymphocytes were separated into two subsets on the basis of relative affinity for sheep red blood cells (E), and these T cell fractions were examined for cytotoxic reactivity against antibody-sensitized Change liver cells (ADCC). High affinity E-rosette-forming cells (E-RFC) (55 +/- 6% of peripheral blood mononuclear cells), capable of rosette formation despite elevated temperatures of incubation (29 degrees C) and a limited concentration of E, contained few antibody-dependent cytotoxic cells (K cells). In contrast, low affinity E-RFC (23+/-7% of mononuclear cell suspensions) requiring cool temperatures of incubation (4 degrees C) and an excess of E to form rosettes, were highly enriched for ADCC activity. The majority of K cells exhibited low affinity interactions with E. T cells in thymus, tonsil, and lymph node formed high affinity E-rosettes and exhibited little reactivity in ADCC. Only peripheral blood and spleen contained easily identified low affinity E-RFC and anti-body-dependent cytotoxic cells. The proportion of low affinity E-RFC in the peripheral blood of normal subjects correlated closely with reactivity in ADCC, making it possible to predict cytotoxic potential for the E-rosette pattern. These data indicate that the human K cell may belong to a previously unappreciated but functionally important subset of thymic dependent mononuclear cells.     

Human monocyte-macrophage-mediated antibody-dependent cytotoxicity to herpes simplex virus-infected cells.

Human peripheral blood mononuclear cells which mediate antibody-dependent cellular cytotoxicity (ADCC) against herpes simplex virus- (HSV) infected target cells consist of both adherent (MA) and nonadherent (MNA) effector cell populations. These two cell populations can be distinguished by their different phagocytic properties and morphologic appearance, their requirement for antibody in the ADCC reaction, and the rapidity with which they lyse target cells in the presence of immune serum. The MA cells are predominantly phagocytic and have the morphologic characteristics of monocyte-macrophages, whereas the MNA cells are nonphagocytic and appear to be small to medium-sized lymphocytes. Optimal expression of ADCC by MA cells requires higher concentrations of immune serum than does MNA cell-mediated ADCC. MA-mediated cell killing is first detectable by 8 hr and reaches completion after 24 hr of incubation. In contrast, MNA-mediated ADCC produces target cell damage by 2 hr and reaches completion at 8 hr of incubation. Unlike MNA effector cells, the MA effector cells are profoundly inhibited after preincubation with either latex or silica particles. The HSV immune status of the donor had no effect on the ability of either cell population to mediate ADCC. These data demonstrate the participation of both nonadherent mononuclear cells, presumably K cells, and monocyte-macrophages, in ADCC directed against HSV-infected target cells.     

Target cell-directed inactivation and IL-2-dependent reactivation of LAK cells

In a previous study, we demonstrated that human natural killer cells (NK) lost their lytic activity after interaction with a sensitive target. The loss of NK activity also led to the loss of antibody-dependent cellular cytotoxicity (ADCC), prompting us to postulate that NK and ADCC activities may result from a common lytic mechanism. In this study, we examined whether nonadherent lymphocytes cultured 7 days in the presence of IL-2 (lymphokine-activated killer (LAK) cells) could also be inactivated and, subsequently, be reactivated in the presence of IL-2. We tested three populations of effector cells (EC): cells isolated from freshly drawn blood and tested immediately, cells cultured with IL-2 for 18 hr, and LAK cells. Once they have interacted with K562, all three cell populations lost greater than 90% of their NK-like lytic activity (NK-CMC) but only 80% of ADCC. However, when we treated the three cell types with antibody-coated K562, they lost 90-99% of NK-CMC and 90-97% of ADCC. In these inactivated effector cells we also observed: (i) a reduction in membrane expression of C-reactive protein; and (ii) a decrease in the expression of Leu-11a when EC were inactivated with antibody-coated K562. The loss of lytic activity against K562 was accompanied by a concomitant loss of activity against other LAK-sensitive targets as well as against antibody-coated targets (ADCC). In competitive inhibition experiments the inactivated effector cells failed to inhibit normal NK-CMC and ADCC activities mediated by fresh NK cells. As we have shown previously, this target-directed inactivation was not due to cell death or to lack of conjugate formation. Inactivated LAK cells regained their lytic potential when cultured with IL-2 and this effect was time dependent. By 72 hr, LAK cells inactivated with K562 regained 99% NK-CMC and 82% ADCC, whereas LAK cells inactivated with antibody-coated K562 regained only 80% NK-CMC and 70% ADCC. When we treated the effector cells with emetine, a potent inhibitor of protein synthesis, we could still inactivate the effector cells with K562 and with antibody-coated K562 but could not reactivate them with IL-2.     

Analysis of effector cells in human antibody-dependent cellular cytotoxicity with murine monoclonal antibodies

We examined purified human large granular lymphocytes, peripheral monocytes, and T cells for their ability to mediate antibody-dependent cellular cytotoxicity (ADCC) with murine monoclonal antibodies. We also evaluated the effects of pretreatment of cells with interleukin 2 and interferon to augment ADCC activity. MB3.6, a murine monoclonal antibody directed against the GD3 ganglioside, induced high levels of ADCC. This ADCC was mediated predominantly, if not completely, by human killer cells (large granular lymphocytes) whereas other effector cell populations demonstrated no significant cytotoxic activity in 6- or 18-hr assays. The IgG2a an anti-melanoma antibody 9.2.27 generated low or no ADCC with most normal donors or melanoma patients. IL 2 was a very potent booster of ADCC activity. Interferon alpha also was effective, whereas interferon gamma did not augment but rather inhibited reactivity. We tested a large panel of antibodies of various isotype against colon carcinoma cells and found that gamma-3 isotype antibodies more frequently generated ADCC and produced higher levels of cytotoxic activity than did IgG1 or IgG2 antibodies. It appears that a variety of parameters can affect ADCC reactions, including the type of effector cell and its level of activation, the isotype of the antibody, and properties of the target cell line such as its susceptibility to lysis.     

Lymphocyte-mediated cytotoxicity to autologous cells infected with measles virus. II. Specificity of the cytotoxic reaction and characterization of the effector cells involved.

The mechanism of lymphocyte-mediated cytotoxicity to cells infected with measles virus was investigated. Cytotoxicity was measured in a direct assay, immediately after the isolation of lymphocytes from human peripheral blood; mononuclear leukocytes, infected with measles virus in vitro, served as autologous target cells. Virus-specific cytotoxicity required the presence of both IgG antibodies against measles virus and of effector lymphocytes. The effector lymphocytes had Fc receptors and were mainly present in a fraction of non-T lymphocytes. Monocytes were not cytotoxic but rather inhibitory. These results indicate that lysis of virus-infected cells in this direct assay is due to antibody-dependent cellular cytotoxicity (ADCC), caused by K cells. Control experiments showed that the virus-infected target cells were sensitive to incubation with human serum or IgG, resulting in a nonspecific increase of ⁵¹Cr release; however, this did not affect the results of K-cell cytotoxicity. Maximal virus-specific lysis by ADCC did not reach the level obtained by complement-dependent cytotoxicity. Possible explanations for this difference are discussed.     

Antibody-dependent cell-mediated cytotoxicity to target cells infected with type 1 and type 2 herpes simplex virus.

The phenomenon of antibody-dependent cell-mediated cytoxicity (ADCC) has been extended to include target cells acutely infected with herpes simplex type 1 virus (HSV-1) or herpes simplex type 2 virus (HSV-2) in an in vitro system that employs immune human serum and human blood mononuclear cells. The cytotoxic reaction was detectable after 1 hr of incubation and was complete between 4 and 8 hr. The amount of ADCC noted was directly proportional to the logarithm(10) of the effector: target cell ratio (E:T), and ADCC was noted at E:T as low as 1:1. The mononuclear effector cell was present in the blood of both HSV immune and non-immune individuals. The immune serum factor was demonstrated to be an antibody with specificity for HSV membrane antigen(s) and was reactive with target cells infected with either of the two HSV types. The antibody rendered the mononuclear cell cytotoxic by sensitization of the target cell rather than by direct attachment to or "arming" of the mononuclear cell. The physiochemical properties of the antibody as well as its presence in cord blood demonstrated that it is an immunoglobulin on the IgG class.     

Surface receptors and immune activity of purified human circulating mononuclear cells. III. The mechanisms of lysis, by lymphocytes and monocytes, of target cells in the lymphocyte-dependent and monocyte-dependent ADCC, NK, NOCC, and MICC cytotoxic reactions

The abilities of unfractionated mononuclear cells (MNC), monocytes (98-99% pure), and lymphocytes (98-99% pure) to carry out the lysis of target cells in the ADCC, NK, NOCC, and MICC assays were compared. Lymphocytes by themselves were able to lyse the CRBC (ADCC), K-562 (NK), and RRBC (MICC) target cells. The monocytes were very effective in the lysis of the CRBC (MICC) target cells. However, the lysis of two other target cells--RRBC (NOCC) and HRBC (ADCC)--required the simultaneous presence of both lymphocytes and monocytes in order to effect optimal lysis. Soluble factor(s) secreted by the cytotoxic cells capable of lysing the target cells were detected only in the NK assay. The activity of the soluble cytotoxic factor (NKCF) was only 25-40% of that exhibited by the cytotoxic NK cells and it was secreted by the cytotoxic cells after 48 hr of culture and not 24 hr of culture which is the usual assay condition. The NKCF was cytotoxic only to the NK target cells and not to the target cells used in the ADCC, NOCC, and MICC cytotoxic assays. Different classes of lymphocytes were cytotoxic in the monocyte-independent assays [ADCC (CRBC), NK (K-562), and MICC (RRBC)]. The null lymphocytes and the T lymphocytes were the primary cytotoxic cells in the ADCC and MICC assays, respectively, whereas the T, B, and null cells were almost equally cytotoxic in the NK assay. With respect to the monocyte-dependent assays [ADCC (HRBC), NOCC (RRBC), and MICC (CRBC)], the cytotoxic activity of any one class of lymphocytes failed to approach that of the unfractionated MNC. The T cells were the most cytotoxic; the B cells exhibited limited cytotoxic activity in only the ADCC assay and the null cells showed no cytotoxic activity. However, the combination of T and non-T cells and, to a lesser extent, T and B cells, exhibited much greater cytotoxic activity than the individual cells and together were as cytotoxic as the unfractionated MNC. It is concluded that, depending upon the selection of the target cells, lysis in the ADCC, NK, NOCC, and MICC assays may be effected by lymphocytes only, by monocytes only, by both monocytes and lymphocytes, or as a result of lymphocyte-monocyte collaboration. In the latter instance more than one class of lymphocytes must be present in order for maximum cytotoxic activity to be expressed.     

E-rosette receptors induced by phytohemagglutinin on human K cells expressing T-cell surface antigens.

Killer cells (K cells) enriched from human blood mononuclear cells which mediate antibody-dependent cellular cytotoxicity (ADCC) were examined for surface markers. Sixty-seven percent of the E-rosette-negative, sIg-negative cells reacted with anti-T cell serum (AMT) previously shown to react with immunochemically defined T-cell antigens. Phytohemagglutinin induced 25% of K cells to express an E-rosette receptor. When these induced cells were isolated, greater than 98% reacted with AMT and 17% expressed the Fc receptor for IgG. Furthermore, they retained their functional capacity in ADCC. These findings demonstrate that an E-rosette receptor can be induced on human K cells. The data suggest the K-cell fraction included a population of thymus-dependent lymphocytes which can function as effector cells in ADCC.     

Inhibition of human killer cells by autologous lymphocytes.

Human antibody-dependent cellular cytotoxicity (ADCC) mediated by K cells is shown in this study to be inhibited by autologous lymphocytes. Inhibitor activity resides in a population of lymphocytes lacking Fc receptors, i.e., depletion of Fc receptor-bearing lymphocytes on immobolized enriches for inhibition. A T cell-enriched population does not inhibit. The effect is not steric inhibition since addition of large numbers of sheep or chicken erythrocytes does not decrease ADCC. Spontaneous cytotoxicity mediated by NK cells in the absence of added antibody is not inhibited by the FcR-depleted population, indicating that K and NK cells differ from each other in this respect.     

The role of apoptosis in antibody-dependent cellular cytotoxicity

Apoptosis in three lymphoma cell lines has been studied following cytotoxicity induced in vitro by normal human blood lymphocytes utilizing either natural killer (NK) or antibody-dependent cellular cytotoxic (ADCC) mechanisms. Guinea-pig L₂C leukaemic lymphocytes, but not the human cell lines Daudi and Jurkat, revealed a degree of time- and temperature-dependent apoptotic death upon simple culture in vitro. NK cytotoxicity at low effector: target ratios (E: T) induced both release of⁵¹Cr and apoptosis. However NK cytotoxicity at higher E : T, and ADCC at all E : T, increased the level of⁵¹Cr release while reducing the level of apoptosis. The findings were consistent with the apoptotic process being cut short by intervention of necrotic death. The same characteristics accompanied ADCC whether the effectors were recruited by Fc regions of antibody coating the targets, or by bispecific antibodies attaching one arm to the targets and the other to Fc receptors type III on effectors. This finding, and the high level of cytotoxicity elicited by the bispecific method, confirm the belief that NK cells, in addition to exerting NK cytotoxicity, represent the principal effectors for ADCC among blood mononuclear cells. Our results suggest that NK cells have both apoptotic and necrotic mechanisms available for killing their targets, but use only the latter for ADCC.     

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.     

Characterization of human K cells by surface antigens and morphology at the single cell level

Human lymphocytes killing bovine erythrocytes in vitro in antibody-mediated reactions were characterized at the effector cell level in the ADCC plaque assay. Five to 10% of highly purified peripheral blood lymphocytes are active K cells in this system. Forty to 50% of these were T gamma cells expressing the T cell-associated surface antigens T3 and Leu-1. These cells also expressed the T8/Leu-2a antigens (approximately 20%) or the T4/Leu-3a antigens. Although approximately 30% of the K cells were T4+ when examined after completion of the ADCC assay (18 hr), only less than 10% were T4+ (and Leu-3a+) when examined before the assay. The results indicated that exposure to antigen/antibody complexes during the assay induced increased T4 expression, probably linked to Fc gamma R modulation on some initially T4-/T3+ lymphocytes. The expression of the other antigens (including Leu-3a) was not affected by exposure of the lymphocytes to antigen/antibody complexes. Two-color fluorescence experiments further demonstrated that a minor fraction (10 to 20%) of the K cells carrying T cell-associated antigens also expressed the monocyte/null cell-associated antigen M1 as detected with the monoclonal antibody OKM1. A second major category of effector cells, composed of at least 25% of the K cells, were large granular lymphocytes (LGL) that lacked detectable T cell-associated antigens but expressed the HNK-1 (Leu-7) as well as the M1 antigen. As seen from the size of the plaques formed by different effector cells, K cells of the LGL type had a greater recycling capacity and/or cytolytic efficiency than those of T gamma type.     

Ultrastructure of antibody dependent cellular cytotoxicity in HSV 1 infected and uninfected Chang liver cells

The binding and ultrastructural features of antibody dependent cellular cytotoxicity (ADCC) mediated by human peripheral blood lymphocytes were studied in herpes simplex virus type I (HSV-1) infected Chang liver (CL) cells plus human anti-HSV-1 serum, and in uninfected CL cells plus guinea pig anti-CL antiserum. Non-cytolytic controls included target cells treated with normal serum in place of sensitized targets and heat shocked lymphocytes instead of normal lymphocytes. By transmission electron microscopy, target cell membranes were either broadly indented by effector cells or locally invaginated by means of effector cell filopodia. In neither case did the indentation appear to break the plasma membrane of the target. Control preparations showed only non-indented areas of simple membrane contact. By scanning electron microscopy, the effector lymphocytes in both the active ADCC and normal serum control preparations had a sparse distribution of short microvilli over their surfaces. The majority of heat shock control lymphocytes appeared normal, but 12-20% demonstrated surface patches devoid of microvilli. The hypothesis that ADCC may involve a three-step process is discussed.     

C3 receptors on human lymphocyte subsets and recruitment of ADCC effector cells by C3 fragments

The presence of C3 receptors on human peripheral blood lymphocytes (PBL) and on the ADCC-exhibiting subset (K cells) thereof was analyzed by rosetting with bovine erythrocytes (Eb) or chicken erythrocytes (Ec) carrying human C3b, C3bi, or C3d. The indicator cells were coated with 20,000 to 100,000 C3 fragments, obtained by C3 activation with purified proteins of the alternative pathway and trypsin treatment. ADCC was studied at the cellular level by means of a plaque assay, with complement-free or complement-carrying indicator cells as targets. Of the total lymphocytes, 12 to 14% bound EC3b; 6 to 8%, EC3bi; and approximately 2%, EC3d. Surface marker analysis indicated that approximately 75% of the C3b-binding lymphocytes in PBL were either B or null cells and approximately 60% of the C3bi-binding cells were T cells, as characterized by the monoclonal antibodies OKT3 and OKT4 or by presence of receptors for Helix pomatia hemagglutinin. Of the K cells, which constituted from 5 to 10% of the total lymphocytes, approximately 20% bound C3b; 30 to 35%, C3bi; and 7 to 8%, C3d. Here the majority of the C3b binders were null cells, and the majority of the C3bi and C3d binders were T cells. Only one-third of the C3b-binding K cells and one-fifth of the C3bi-binding K cells bound both fragments. The nature of these double binding cells is unknown. In contrast, all C3d-binding K cells bound C3bi as well. C3 fragment-carrying target cells did not induce K cell-mediated lysis in the absence of anti-target antibodies but strongly enhanced ADCC in the presence of sublytic concentrations of such antibodies. The rank order for C3 fragment-induced enhancement was C3bi greater than C3d greater than C3b. It reflected the relative proportions of effector cells binding the different fragments. Enhancement was the expression of effector cell recruitment rather than of increased cytolytic activity of individual K cells. This recruitment was selective in that C3b-carrying target cells primarily recruited effector cells of null type, binding C3b, while C3bi- or C3d-carrying targets primarily recruited C3bi and/or C3d-binding K cells of T gamma type. Thus, these experiments show directly at the effector cell level that cell-bound C3 fragments constitute important recognition structures, which strongly amplify ADCC both by recruiting the proper effector cells into the cytolytic reaction and by very significantly decreasing the antibody concentration needed for its induction.     

A rapid method for the isolation of human peripheral null lymphocytes.

We describe here a new technique for the isolation of human peripheral null lymphocytes: cells lacking detectable surface immunoglobulin as well as receptors for sheep erythrocytes. The double rosette technique described employs a combined negative selection for Ig⁺ cells by specific anti-Ig-coated sheep erythrocytes and E rosette selection for T cells. This singlestep procedure facilitates the isolation of null cells from large cell populations and can be completed in less than 2 hr. The isolated null subpopulation represents less than 5% of the total peripheral mononuclear cells and is at least 85–90% pure by sensitive surface marker analysis. The null subpopulation is shown to be highly enriched for effectors of both antibody-dependent cytotoxicity against autologous lymphocytes and spontaneous cytotoxicity against the K562 leukemia blast cell line. Application of this technique will allow further characterization of the effector populations for ADCC and NK as well as differentiation of T and B cell precursors.     

Divergence in activation by poly I:C of human natural killer and killer cells

Summary Interferons consistently enhance spontaneous cellular cytotoxicity (SCC) mediated by natural killer (NK) cells. More controversial is the ability of interferons to enhance antibody-dependent cellular cytotoxicity (ADCC) mediated by killer (K) cells. Since NK and K cells appear to represent overlapping subpopulations of lymphocytes, the present study was undertaken to examine in greater detail the relationship between NK and K cell functional modulation by the potent interferon inducer, poly I:C. Utilizing peripheral mononuclear cells from a panel of 21 healthy individuals, treatment in vitro with poly I:C resulted in modulation of both SCC and ADCC. SCC was significantly enhanced in 52 of a series of 55 trials (95%), whereas ADCC was significantly enhanced in parallel in only 18 of the trials (33%). Cells which mediated enhanced ADCC were plastic-nonadherent, which is characteristic of K cells. SCC was consistently enhanced in all but two of the 14 individuals who were tested two or more times. By contrast, the ability of poly I:C to enhance ADCC varied between trials in 11 of these individuals. In the other three, ADCC enhancement never occurred. No correlation existed between SCC and ADCC augmentation despite use of the same target cell to assess the two lytic activities in parallel. Poly I:C exclusively enhanced SCC in 36 trials (65%) and exclusively enhanced ADCC in two trials (4%). Discordance between SCC and ADCC enhancement also occurred in three of eight trials (38%) in which lymphocytes were treated directly with interferon a. Results in long-term (18-h) ⁵¹Cr-release assays indicated that poly I:C accelerated the kinetics of ADCC without affecting the proportion of target cells lysed by K cells. By contrast, an increased proportion of target cells was killed by poly I:C-stimulated NK cells. These results suggest that the controversy concerning relative interferon effects upon NK and K cells derives from differences both quantitative and qualitative in nature. K cell activity is enhanced but at a relatively low frequency. Enhancement of NK cell activity is selective in the sense that it occurs independently of and with greater frequency than enhancement of K cell activity. Distinct biological mechanisms may, therefore, be involved in regulation and expression of NK and K cell activation by interferons.     

Dissociation of autologous and allogeneic mixed lymphocyte reactivity by using a monoclonal antibody specific for human T helper cells

A monoclonal antibody defining a population of human T helper cells was developed and shown to specifically block the autologous mixed lymphocyte reaction (AMLR). This antibody, termed KT69-7 (IgG1), recognized 62% of peripheral blood E rosette-positive (E+) cells while demonstrating negligible reactivity with E- cells, monocytes, granulocytes, EBV-transformed B cell lines, and mouse splenocytes. Separation of E+ cells into KT69-7+ and KT69-7- populations revealed that KT69-7+ T cells provided helper function in PWM-driven B cell differentiation, whereas KT69-7- T cells provided no help and may suppress this response. Modulation of membrane moieties by using KT69-7 or OKT4 plus goat anti-mouse IgG removed reactivity to both these antibodies, suggesting an association between these molecules recognized by these antibodies. In functional studies, KT69-7 selectively blocked the AMLR while demonstrating minimal or no effect on the allogeneic MLR (allo-MLR). Blocking of the autoreactivity occurred when either autologous B lymphocytes or macrophages were used as stimulators. The failure of KT69-7 to block the allo-MLR was not attributable to excessive allogeneic stimulus; KT69-7 failed to block even under conditions of limiting numbers of stimulator cells. KT69-7 thus appears to recognize a molecule on the surface of T helper cells required for recognition of autologous class II antigens.