Ia-positive T lymphocytes are the producer cells of interferon gamma

The production of γ-interferon (IFNγ) in human peripheral blood T lymphocytes was induced by stimulation with PHA. For identification of the producer cell of IFNγ, double fluorescence studies were undertaken and titers of interferon were determined in preparatively separated T-cell subpopulations reactive with one of the monoclonal antibodies OKT3, OKT4, OKT8, and OKIa1. Production of IFNγ was found in OKT3⁺, OKT4⁺, and OKT8⁺ cells. However, IFNγ production occurred only in T cells also reactive with the monoclonal antibody OKIa1. Addition of macrophages had no substantial effect on interferon titers in these subpopulations. It is suggested that the T cell subset producing IFNγ is characterized by its reactivity with the monoclonal antibodies OKT3, OKT4 or OKT8, and OKIa1.     

Synthesis of alpha and gamma interferons by a human cutaneous lymphoma with helper T-cell phenotype

A cloned human cutaneous lymphoma Hut102-B2 with helper T-cell phenotype (Leu1⁺, Leu2a^?, Leu3a⁺) was found to produce substantial quantities of interferon (IFN) on induction with the phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA). Whereas only trace amounts of IFN were secreted by Hut102-B2 cells spontaneously, up to 8000 laboratory units/ ml of IFN were synthesized under the optimal conditions of TPA induction. Characterization studies including neutralization by specific antisera to IFNs and determination of the activities in human and bovine cells disclosed that the IFN produced by Hut102-B2 cells exposed to TPA was a mixture of immune IFN (IFN-γ) and leukocyte IFN (IFN-α) made in approximately equal amounts in terms of antiviral activity.     

The regulation of gamma-interferon production by interleukins 1 and 2

Purified interleukins 1 and 2 (IL-1 and IL-2) were used to investigate their role in the production of gamma-interferon (gamma-IFN). Macrophage depletion from human peripheral blood mononuclear leukocytes (PBML) inhibited gamma-IFN production. Addition of purified IL-1 partially restored IFN production of macrophage-depleted PBML induced by three T cell mitogens (phytohemagglutinin, PHA; concanavalin A, con A; and staphylococcal enterotoxin A, SEA), but had no effect on induction of IFN production by undepleted PBML. Therefore endogenous IL-1 production by macrophages is probably one of the mechanisms by which they act as accessory cells for IFN production by lymphocytes. A monoclonal antibody 9.6 which binds to the sheep erythrocyte (E) receptor found on human T cells inhibited IFN production. Addition of IL-2, but not IL-1, was found to reverse this inhibition. Prostaglandin E2, a macrophage product, inhibited gamma-IFN production induced by PHA, Con A, and OKT3 but usually not SEA. This inhibitory effect was reversible by the addition of IL-2 but not IL-1. In the absence of mitogen IL-1 alone rarely induced any IFN production, although some IFN was produced by PBML from a small minority of donors. Without mitogen IL-2 induced IFN production only at very high concentrations and the added presence of IL-1 did not enhance this induction.     

Molecular interactions in human T-cell-mediated cytotoxicity to Epstein-Barr virus. I. Blocking of effector cell function by monoclonal antibody OKT3

The ability of different anti-human T-cell lymphocyte monoclonal antibodies to inhibit the effector function of the cytotoxic T-cell response against autologous Epstein-Barr virus (EBV)-infected B-cell targets has been tested. It was found that monoclonal antibody, OKT3, which reacts with most human T cells, blocks the effector cell function in the absence of complement, an effect that was dose dependent. When monoclonal antibody OKT3 was tested at a concentration of 1 μg/ml, inhibition of cytotoxicity ranged between 50 and 80%. The F(ab′)₂ fragment of OKT3 inhibited as well as the intact IgG molecule, indicating that the Fc portion of the antibody is not necessary for the cytotoxicity blocking. The Fab fragment of OKT3 had lower blocking activity per microgram of protein tested. Antibodies SC1, OKT11 (anti-pan T cell), OKT8 (anti-cytotoxic/suppressor subset), and L368 (anti-HLA) did not have any discernible blocking effects. However, antibodies SC1, OKT8, and L368 could abrogate the cytotoxic activity in the presence of complement. Blocking by OKT3 was not due to its being present on the cell surface in higher concentrations than the other monoclonal antibodies since cytofluorographic analysis demonstrated that the amount of OKT8 or L368 antibodies bound on the cells was greater than OKT3. In addition, blocking was not due to antigenic modulation since incubation with antibody OKT3-F(ab′)₂ was not associated with a significant decrease in the amount of its reactive antigen. Under the conditions tested OKT3 did not affect cell viability or cause agglutination.     

Phenotypic Analysis of New World Primate Mononuclear Cell Surface Antigens

We have applied a panel of monoclonal antibodies against antigens present on the surface of human mononuclear cells to the study of mononuclear cell surface antigens expressed by seven species of New World primates. Antibodies to the sheep erythrocyte receptor (OKT11a) to a thymocyte antigen (OKT10), to the I region of the major histocompatibility locus (OKIa), and to an antigen found on the surface of human monocytes (OKM1) cross-reacted with mononuclear cell surface antigens of most of the species studied. Antibodies to antigens which have been correlated with functional capabilities in the human system (OKT4, OKT5, OKT8, 3A1) were much less reactive with platyrrhine mononuclear cells. These reagents may be quite useful in studies of primate phylogeny and immunology.     

Monoclonal antibody OKT11A inhibits and recombinant interleukin 2 (IL 2) augments expression of IL 2 receptors at a pretranslational level

The expression of receptors for interleukin 2 (IL 2) represents a critical event regulating the growth of normal T lymphocytes. We investigated the effects of the inhibitory monoclonal antibody OKT11A (anti-sheep erythrocyte receptor) and of purified recombinant IL 2 (rIL 2) on the expression of IL 2 receptors by activated T cells at both the protein and the mRNA levels. Adding OKT11A antibody (0.5 microgram/ml) to phytohemagglutinin (PHA)-stimulated cultures of human peripheral blood mononuclear cells (PBMC) markedly suppressed cellular proliferation (assessed by [3H]thymidine incorporation) and IL 2 receptor expression (determined by immunofluorescence assay by using the anti-IL 2-receptor antibody, anti-Tac). Northern blot analysis performed with the use of a cDNA probe specific for the human IL 2 receptor gene demonstrated that OKT11A antibody also decreased the accumulation of IL 2 receptor mRNA induced by PHA in PBMC. Purified rIL 2 (10 U/ml) alone had little effect on the expression of IL 2 receptors in unstimulated PBMC cultures. In combination with PHA or with PHA plus OKT11A, however, rIL 2 augmented both the expression of IL 2 receptor protein on PBMC and the accumulation of IL 2 receptor mRNA in PBMC. Adding anti-Tac antibody to PBMC cultures to block the interaction of IL 2 with its receptor diminished the accumulation of IL 2 receptor mRNA induced by PHA. Taken together, these data demonstrate that OKT11A antibody inhibits and IL 2 augments expression of IL 2 receptors on PHA-stimulated T cells, at least in part, at a pretranslational level.     

Capping of the surface OKT3 binding molecule prevents the T-cell proliferative response to antigens: evidence that this molecule conveys the activation signal

The human T-lymphocyte receptor for antigen appears to have been localized to a cluster of associated surface glycoprotein molecules, among which is the OKT3 binding molecule. We have tested the hypothesis that selective removal of the OKT3 binding molecule eliminates the cellular immune response to antigens by clearing the surface of the molecule that conveys the activation signal. Enriched T cells were obtained from donors immune to purified protein derivative (PPD), streptokinase-streptodornase (SK-SD), or keyhole limpet hemocyanin (KLH). T-3 molecules were cleared from the cell surface by capping with OKT3 and F(ab')2 goat anti-mouse IgG. Regeneration of surface molecules was prevented by culturing the T-3 capped cells with OKT3 625 ng/ml. The capacity of capped T cells to proliferate in culture with antibody in response to antigens, alloantigens, and the mitogens, PHA and ionophore A23187, was compared to uncapped cells pretreated with media and to capped cells permitted to regenerate the OKT3 binding molecule. T-3 capped cells cultured in the presence of antibody failed to proliferate to antigens or alloantigens. However, T-3 capped cells cocultured with antibody also did not significantly proliferate to PHA, but did respond to A23187. In contrast, both media-treated T cells and cells which had regenerated the OKT3 binding molecule proliferated to mitogens, antigens, or alloantigens. The requirement for the OKT3 binding molecule was determined by utilizing T-1, T-4, and T-8 capped cells. T-1, T-4, or T-8 capped cells cultured in the presence of OKT1, OKT4, or OKT8 proliferated in response to antigens, alloantigens, and mitogens. These results demonstrate that in the absence of the OKT3 binding molecule, antigens, alloantigens, and PHA failed to induce a significant cellular proliferative response. In the absence of this molecule, PHA cannot bind to its carbohydrate moiety, and therefore cannot activate T cells to proliferate. These data support the concept that the molecule binding OKT3 conveys the transmembrane signal resulting in cellular activation.     

The recognition specificity of a murine helper T cell for hemagglutinin of influenza virus A/PR/8/34

Human large granular lymphocytes (LGL), which are known to be responsible for natural killer (NK) cell activity, also produced a variety of lymphokines including interleukin 2 (IL 2), colony stimulating factor (CSF), and interferon (IFN) in response to phytohemagglutinin (PHA) or concanavalin A (Con A). Human peripheral blood LGL, which were purified by removal of monocytes adhering to plastic flasks and nylon columns, followed by separation on a discontinuous Percoll gradient, and additional treatment with anti-OKT3 and Leu-M1 plus complement, were more potent producers of these lymphokines than unseparated mononuclear cells (MNC), nylon column-eluted cells, or purified T lymphocytes. Moreover, IL 2 production by LGL could be further distinguished in that it was not enhanced by the addition of macrophages or macrophage-derived factor, i.e., IL 1, whereas addition of macrophages did potentiate IL 2 production by T lymphocytes. Further analysis of cells in the LGL population using various monoclonal antibodies revealed that removal of cells with OKT11 or AF-10, a monoclonal antibody against human HLA-DR antigen, decreased IL 2 production, whereas removal of OKT8+, OKM1+, Leu-M1+, or Leu-7+ cells led to enhanced IL 2 production. The LGL population is therefore heterogeneous and includes at least three functionally and phenotypically distinct subsets. An atypical T cell subset (OKT3-, Leu-1-, OKT11+) rather than the myeloid subset of LGL (Leu-M1+ or OKMI+) was the source of LGL-derived IL 2, whereas the latter subset and/or another subset of OKT8+ cells appear to regulate this IL 2 production. In addition to performing NK activity, LGL on a per cell basis seem to be more effective than T lymphocytes in producing lymphokines, namely, IL2, CSF, and IFN.     

Vitamin D receptor expression in human lymphocytes. Signal requirements and characterization by western blots and DNA sequencing.

The signals controlling the expression of the receptor protein for 1 alpha,25-dihydroxyvitamin D3 in normal human lymphocytes and the relationship of this protein to the classical vitamin D receptor were examined. Lymphocytes activated with the OKT3 antibody to the T-cell antigen receptor expressed fewer binding sites as compared to lymphocytes that were activated by the polyclonal activator phytohemagglutinin (PHA). However, combination of OKT3 and phorbol myristate acetate produced a concentration of binding sites similar to the PHA-activated cells. The receptor from OKT3 and OKT3 + phorbol myristate acetate-activated lymphocytes exhibited decreased binding to DNA-cellulose compared to PHA-activated lymphocytes. In lymphocytes activated either by PHA or OKT3 (but not in resting cells), a 50-kDa species cross-reacting with a monoclonal antibody against the intestinal vitamin D receptor was detected. Finally, RNA from activated lymphocytes was amplified by polymerase chain reaction using oligonucleotide primers flanking the 196 base pair long region encoding the DNA-binding domain of the human intestinal receptor. The amplified product showed an identical nucleotide sequence to the DNA-binding domain of the human intestinal receptor. These findings suggest that expression of the 1,25-(OH)2D3 receptor in lymphocytes is triggered by distinct and contingent signals, and that the protein and the mRNA encoding it are identical to the classical vitamin D receptor.     

Monoclonal antibodies to the CD5 antigen can provide the necessary second signal for activation of isolated resting T cells by solid-phase-bound OKT3

Activation of human peripheral blood T cells by the anti-CD3 antibody OKT3 has been shown to require not only cross-linking of CD3 molecules with multimeric binding of the Fc part of OKT3 to a solid support, but also a second accessory cell-provided signal. Accordingly, measurement of T cell activation in cultures of highly enriched T cells with solid-phase-bound OKT3 can be used to investigate whether other agents can replace accessory cells. In this study we examined the capacity of anti-CD5 monoclonal antibodies to provide the additional activation signal. Resting T cells were prepared by isolating E rosette-positive cells, by removing OKM1(+) and HLA-DR(+) cells by panning, and by subsequent treatment of the cells with L-leucine methyl ester to kill remaining monocytes. These T cells were unresponsive to phytohemagglutinin (PHA) or to solid-phase-bound OKT3. However, when cultured in the presence of an anti-CD5 monoclonal antibody (anti-Leu-1, OKT1, or anti-T1), a proliferative response to solid-phase-bound OKT3 (but not to soluble OKT3 or to PHA) was observed. Anti-CD5 had no functional effect by itself, but in association with solid-phase-bound OKT3 it enhanced IL 2 receptor expression and IL 2 production and it initiated T cell proliferation. T cell proliferation under these conditions could be inhibited by an IL 2 receptor blocking antibody anti-Tac, thus confirming that anti-CD5 provides the second signal for an IL 2-dependent pathway of T cell proliferation. Preincubation of T cells with anti-Leu-1 or OKT1 resulted in complete loss of CD5 antigenicity, and such CD5 modulation was sufficient to induce a proliferative response to solid-phase-bound OKT3. It is concluded that in T cell activation by solid-phase-bound OKT3 the necessary additional signal can be provided by modulation of the CD5 antigen with an anti-CD5 antibody. CD5 therefore appears to be a positive signal receptor on the T cell membrane, whose physiologic ligand still has to be determined.     

In vitro OKT3-induced mitogenesis in selenium-deficient patients on a diet for phenylketonuria

Patients with phenylketonuria (PKU) are frequently deficient in the essential trace element selenium (Se), because of their very low protein diet. Using two approaches to investigate T-cell response to proliferative signaling, viz, mitogenesis caused by the monoclonal antibody OKT3 and the plant lectin phytohaemagglutinin (PHA), we demonstrated significantly reduced responses to optimal concentrations of OKT3 in a group of PKU patients with reduced serum Se compared with a normal group (p = 0.0005) and with a group of PKU patients whose serum Se was normal (p = 0.0023). The response of the Se-deficient group to optimal levels of PHA did not differ from that of the normal controls or from that of Se-normal PKU patients. A dose-dependent relationship between serum Se levels and mitogenic response was evident for OKT3 (r = 0.34, p = 0.0154), but not for PHA (r = -0.02, p = 0.9086). We suggest that the reduced response to OKT3 mitogenesis in Se-deficient PKU patients is possibly the consequence of impaired Se-dependent metabolic activity, which affects mitogenic signaling via the T cell antigen receptor (TCR/CD3) complex.     

Suppressor T cell activation by human leukocyte interferon

Murine fibroblast interferon (IFN beta) activates murine suppressor T lymphocytes in vitro, which suppress plaque-forming cell responses by spleen cells. Suppression of human in vitro immune responses by IFN was investigated to determine whether human IFN also activates suppressor T cells. Human leukocyte IFN (IFN alpha) suppressed pokeweed mitogen-induced polyclonal immunoglobulin production by human peripheral blood mononuclear cells (PBMC) by 80 to 90% at doses of 200 to 350 U/ml. Responses by IFN alpha-treated PBMC were suppressed in a dose-dependent manner; control cultures had maximal responses on day 7. PBMC incubated with 10,000 U/ml of IFN alpha contained activated suppressor cells that decreased pokeweed mitogen-stimulated, polyclonal immunoglobulin production by autologous cells by 70 to 80%. Suppression mediated by these cells was prevented by catalase, ascorbic acid, and 2-mercaptoethanol (2-ME). In murine systems, these reagents interfere with expression of suppressor T cell activity by preventing activation of soluble immune response suppressor. Selection procedures with monoclonal antibodies identified the suppressor cell as an OKT8+ (suppressor/cytotoxic) T lymphocyte. Selected OKT8+ cells required less IFN alpha (1000 U/ml) for activation and were effective in smaller numbers than unfractionated activated PBMC. IFN alpha-activated suppressor cells also inhibited proliferation in mixed lymphocyte and mitogen-stimulated PBMC cultures; again, catalase and 2-ME blocked suppression. These results indicate that IFN alpha activates suppressor T cells in human PBMC cultures; the ability of catalase, 2-ME, and ascorbic acid to block suppression suggests that these suppressor T cells have certain similarities to IFN beta or to concanavalin A-activated murine suppressor T cells.     

E-rosette formation at 37 °C: Analysis with monoclonal OKT antibodies

When cultured in the presence of PHA, a proportion of human peripheral blood mononuclear cells acquires the capacity to form E rosettes with sheep erythrocytes that are resistant to incubation at 37 °C. The nature of this 37 °C stable E-rosette formation was investigated using a panel of monoclonal OKT antibodies directed to human T-lymphocyte surface antigens. OKT11A antibody, at a concentration of 0.2–0.4 μg/ml, markedly blocked 37 °C E rosetting. OKT1, OKT3, OKT4, OKT6, and OKT8 antibodies, when tested at 10 μg/ml, show no such inhibiting activity. Quantitative studies with ¹²⁵I-labeled OKT11A indicated that the antibody interacted strongly with both 37 °C E-rosetting and nonrosetting cells, the association constant being 1.6–2.0 × 10⁹M^?1. However, on the average, a threefold higher concentration of OKT11A receptor sites was found on 37 °C E-rosette-forming cells (14.8 × 10⁴ sites/cell) than on nonrosetting cells (4.8 × 10⁴ sites/cell). Our data suggest that 37 °C E-rosette formation is governed by a lymphocyte surface determinant recognized by OKT11A antibody. “Overexpression” of OKT11A antigenic sites on a proportion of PHA-stimulated lymphocytes may explain their capacity to form 37 °C stable E-rosettes.     

The anti-T cell monoclonal antibody 9.3 (anti-CD28) provides a helper signal and bypasses the need for accessory cells in T cell activation with immobilized anti-CD3 and mitogens

CD28 is an antigen of 44 kDa which is expressed on the membrane of the majority of human T cells. The present study examines the functional effects of an anti-CD28 monoclonal antibody (mAb 9.3) on T cell activation induced with immobilized anti-CD3 mAb OKT3 or with mitogens, in the absence of accessory cells. To this end, we used blood resting T cells that were completely depleted of accessory cells (monocytes, B cells, and natural killer cells), and consequently did not respond to recombinant interleukin-2 (rIL-2), to immobilized OKT3, to PHA, or to Con A. Addition of mAb 9.3 to the cultures enhanced IL-2 receptor expression (Tac antigen) on PHA- or immobilized OKT3-stimulated T cells and induced IL-2 receptors on Con A-stimulated T cells. Moreover, addition of mAb 9.3 to cultures of T cells stimulated with PHA, Con A, or immobilized OKT3 resulted in IL-2 production. Soluble mAb 9.3 was a sufficient helper signal for T cell proliferation in response to PHA or immobilized OKT3. Crosslinking of mAb 9.3 by culture on anti-mouse IgG-coated plates enhanced the helper effect and was an essential requirement for the induction of T cell proliferation in response to Con A. No other anti-T cell mAb (anti-CD2, -CD4, -CD5, -CD7, -CD8) was found to provide a complete accessory signal for PHA or Con A stimulation of purified T cells. T cell proliferation induced by the combination of PHA and mAb 9.3 was strongly inhibited by the anti-IL-2 receptor mAb anti-Tac. In conclusion, mAb 9.3 can provide a signal bypassing monocyte requirement in T cell activation with immobilized OKT3, PHA, and Con A, resulting in an autocrine IL-2-dependent pathway of proliferation.     

Adenosine deaminase and immunodeficiency: An in vitro model

We have examined the effect of adenosine and EHNA, a competitive inhibitor of adenosine deaminase (ADA), upon the ability of human peripheral blood lymphocytes to respond to mitogen. Addition of adenosine at concentrations greater than 10 μm (10^?5m) resulted in inhibition of lymphocyte proliferation at 48 hr of culture, provided that the culture medium was relatively free of ADA activity. The actual concentrations of adenosine remaining in inhibited cultures at the time of harvest were considerably lower than those added initially. EHNA alone also inhibited PHA response (and to a lesser extent PWM and Con A responses), but only at high concentrations. Noninhibitory concentrations of EHNA and adenosine together acted synergistically to produce profound inhibition of lymphocyte proliferation. This may provide an in vitro model to explore further the mechanism of the immunodeficiency associated with deficiency of ADA. Adenosine deaminase activity in stimulated cultures did not differ significantly from that found in unstimulated cultures, and the activity per protein or per DNA actually decreased in stimulated versus unstimulated cultures.     

Early events during the activation of human lymphocytes by the mitogenic monoclonal antibody OKT3

The effects of the mitogenic monoclonal antibody OKT3 on the metabolic changes preceding DNA synthesis during the activation of human peripheral blood mononuclear cells were compared with those induced by PHA. The aspects studied included uridine transport, the incorporation of inositol into phospholipids, Na+-dependent amino acid uptake, and protein synthesis. All four parameters were increased in response to the ligation of the T lymphocyte receptor recognized by OKT3. These changes were apparent as early as the corresponding changes induced by PHA. However, the increases in uridine uptake and inositol incorporation were disproportionately reduced when compared to those caused by PHA, and no evidence of high-dose inhibition was seen in cells activated by OKT3. This suggests that at least some lectin-induced changes in metabolism are mediated through additional mechanisms, probably involving distinct receptors.     

Induction of phenotypic differentiation, interleukin 2 production, and PHA responsiveness of "immature" human thymocytes by interleukin 1 and phorbol ester

Small human thymocytes (ST) representing 70% of the thymocytes were isolated according to size by centrifugal elutriation. Although these ST contained approximately 30% PNA-cells, they failed to respond to lectins, indicating the existence of a PNA-ST subset that can be considered to belong to the "immature" thymocyte population. The ST were induced to proliferate if, in addition to PHA, IL 1-containing supernatants of highly purified monocyte cultures or 12-O-tetradecanoyl-phorbol-13-acetate (TPA) were present. The incubation of the ST for 90 hr with TPA or IL 1 in the absence of PHA resulted in a strong reduction in the percentage of cells reacting with the immature thymocyte markers TdT and PNA. In addition, the OKT6+ cells were partially reduced after incubation with IL 1. Concomitantly, an increase in the percentage of cells reacting with the mature T cell markers OKT1 and OKT3 was observed, whereas HLA antigens became strongly expressed on all ST. Although IL 1 or TPA were unable to induce proliferation of the ST, these substances induced IL 2 production by these cells. These shifts to cells with more "mature" phenotypes that are able to produce IL 2 were not observed if the ST were incubated with PHA or culture medium only. The responder capacity of the ST to PHA plus TPA was not significantly affected by the depletion of the more "mature" OKT3+ and OKT1+ cells. In addition, in this situation OKT1+, OKT3+, OKT6- cells were found to be generated from OKT1-, OKT3-, OKT6+ cells. Therefore, it could be excluded that the proliferative responses were due to a selective expansion of a preexisting mature T cell population. Our results indicate that TPA mimics IL 1 in the induction of differentiation of the ST to a stage in which subpopulations of these cells are able to produce IL 2 and to respond to PHA. Because only the proliferating ST were found to react with a monoclonal antibody, which is thought to be directed at the IL 2 receptor (anti-Tac), our data suggest that PHA is required for the induction of expression of receptors for IL 2 in those ST subpopulations that are able to proliferate in the presence of IL 2 generated in situ.     

Interactions of lectins and monoclonal antibodies with human mononuclear cells. I. Specific inhibition of OKT4 and OKT8 binding by Ricinus communis agglutinin and wheat germ agglutinin

We used flow cytometry to examine effects of lectins on interactions between human lymphocytes and the anti-T cell monoclonal reagents OKT4 (T helper-specific) and OKT8 (T suppressor-specific). Wheat germ agglutinin (WGA) inhibited OKT8 binding to lymphocytes by a mean 77% and Ricinus communis agglutinin (RCA-I) inhibited OKT4 binding by 66%. Inhibition was abolished in each case by appropriate carbohydrate hapten inhibitors of lectin binding, indicating it was mediated by the lectin saccharide combining sites. Neither WGA nor RCA-I inhibited binding of OKT3, a pan-T cell monoclonal reagent. In addition, a group of other lectins with a variety of nominal carbohydrate specificities did not inhibit OKT4 or OKT8 binding. Preincubation experiments and gel filtration indicated that inhibition in each case was due to competition between lectin and monoclonal for binding to cell surfaces, not to direct lectin-monoclonal antibody interactions. Treatment of lymphoid cells with OKT8 and complement reduced OKT8- and WGA-binding cells concurrently, whereas treatment with OKT4 and complement did not reduce percentages of either type of cell. Similarly, specific depletion of OKT8-binding cells abolished the mitogenic response to WGA but not that to PHA. Cell populations enriched for WGA-binding cells prepared by flow cytometry and cell sorting demonstrated parallel enrichment for OKT8-binding and depletion of OKT4-binding cells. Therefore, these data demonstrate specific inhibition of OKT4 and OKT8 binding by the lectins, RCA-I and WGA, respectively. Inhibition was mediated by lectin binding to lymphoid cell surfaces, perhaps directly to the T4 or T8 antigens. The observations indicate that lectins may prove useful for investigating structural features of some immunologic cell surface markers. Furthermore, they provide the possibility that certain in vitro effects of lectins on immune function may result from their interactions with molecules such as the T4 and T8 antigens.     

Human T lymphocyte activation by monoclonal antibodies; OKT3, but not UCHT1, triggers mitogenesis via an interleukin 2-dependent mechanism

OKT3 and UCHT1 monoclonal antibodies, which recognize the same human T cell surface antigen, induce proliferation in T lymphocytes. In this report, we compared the mechanism by which these antibodies trigger DNA synthesis in human peripheral blood mononuclear cell (PBMC) cultures. Whereas PBMC from all donors tested were mitogenically inducible by OKT3, cells from only 25 of 40 donors were responsive to UCHT1 . UCHT1 treatment of PBMC from responders, but not from nonresponders, resulted in the expression by T cells of membrane binding sites reactive with anti-Tac monoclonal antibody, which specifies the human interleukin 2 (IL 2) receptor. UCHT1 -induced PBMC supernatants from nonresponders, but unexpectedly, also from responders, contained no measurable IL 2 activity. In keeping with this finding, anti-Tac monoclonal antibody failed to suppress UCHT1 -triggered [3H]thymidine incorporation into PBMC from responsive donors. By contrast, OKT3 treatment of PBMC from all donors led to the emergence of IL 2 receptors, and substantial IL 2 production, and the resultant DNA synthesis was inhibitable by anti-Tac antibody. These data indicate that the interaction of OKT3 and UCHT1 monoclonal antibodies with the same T cell structure leads to the induction of proliferation via two different mechanisms: one dependent on the availability of IL 2 (OKT3) and one independent on the production and processing of this lymphokine ( UCHT1 ). PBMC unresponsiveness to UCHT1 could therefore not be related to a dysfunction in IL 2 synthesis or IL 2 receptor display.     

Modulation of T lymphocyte differentiation antigens: influence of aging

In vitro modulation of human T lymphocyte surface differentiation antigens T3, T8, and T4, by their respective monoclonal antibodies, was studied as a function of donor age. Kinetic studies performed on lymphocytes from young adults indicated that modulation is dependent on concentration of antibody used and duration of culture. OKT3 modulates T3 rapidly (maximum at less than 24 hr) and relatively completely (79% at the highest concentration of antibody used). By 48 hr, regeneration of the T3 antigen is apparent. T8 modulation by OKT8 is slower (continued modulation at 48 hr) and less complete than is T3 modulation by OKT3. OKT4 does not modulate the T4 antigen. In elderly individuals modulation of T3 by OKT3 is preserved whereas modulation of T8 by OKT8 is significantly reduced (24 +/- 8% at 48 hr vs 53 +/- 4% for young controls). These observations document further age-related changes in properties of human T suppressor cells.