Growth and characterization of T cell colonies from human thymus

A semisolid microculture system was used to study T cell colonies grown from human thymocytes. Colony growth was absolutely dependent upon media conditioned by peripheral blood leukocytes (PBL) in the presence of phytohemagglutinin. Plating efficiency was further enhanced by the addition of a non-T, adherent, radiation-resistant (7500 rad) PBL subpopulation, but was not enhanced by culture supernatants of these cells. The T colony precursor cell in the thymus occurred with a frequency of 8.0 X 10(-3) and had a surface receptor for the OKT3 monoclonal antibody. Thymocyte colony cells were functionally distinct from PBL and the major thymocyte population. The colony cells proliferated in response to T cell mitogens, but only in the presence of exogenous growth factors. The cells stimulated normal PBL in mixed leukocyte culture (MLC), but did not respond to alloantigens in MLC or in assays of spontaneous cytotoxicity. This culture system should prove helpful in the study of human thymocyte differentiation.     

Accessory cell competence of ovine oligodendrocytes in mitogenic activation of human peripheral T cells

The multiple sclerosis (MS) plaque is characterized by mononuclear inflammatory cell infiltration, demyelination, loss of oligodendrocytes (OGC), and proliferation of astrocytes. Although antigen-specific, Ia-dependent cellular immune mechanisms have been sought in plaque pathogenesis, Ia-independent T cell activation has not been actively investigated. We examined a potential role of OGC in accessory cell-dependent T cell mitogenesis with the anti-T3 monoclonal antibody OKT3. OGC isolated from ovine white matter on sucrose density gradients were uniformly negative for esterase activity, unlike ovine monocytes. Purified human T cells did not exhibit significant proliferation in 3-day cultures with OKT3, autologous peripheral blood adherent cells (PBAC), or ovine OGC. When T cells were cultured with either PABC or OGC in the presence of OKT3, brisk mitogenesis was observed. Thus, OGC have the capacity to function as accessory cells in the mitogen-induced proliferation of T cells.     

Monoclonal antibodies against T cell differentiation antigens initiate stimulation of monocyte/macrophage oxidative metabolism

Within the first minute after incubation with the mouse anti-human T cell orthoclone monoclonal antibodies OKT3, OKT4, and OKT8, and in the absence of complement, human monocytes generate a burst of highly reactive oxygen metabolites as detected by a luminol-dependent photometric chemiluminescence (CL) assay. The kinetics of the CL responses to these antibodies are identical to that induced by OKM1, the monoclonal antibody to human monocytes and granulocytes. With regard to CL response intensities, OKM1 induces the maximal response and those of OKT3, OKT4, and OKT8 closely reflect the proportion of T cell subsets recognized by these antibodies in peripheral blood. This reaction is also observed when monoclonal antibodies against mouse Lyt surface determinants (Lyt-1 and Lyt-2) and Thy-1 antigen are tested against murine spleen cells. This murine model was further used to investigate the specificity and the mechanism of this reaction. It was demonstrated that the CL response is Lyt antigen specific, occurs upon addition of monoclonal IgG but not IgM antibodies, requires the concomitant presence of CL-producing cells (CLPC) (promonocytes, monocytes, macrophages, and/or granulocytes) and of fully differentiated T cells, and lastly, is mediated via a T cell opsonization process. Selective blockade of bone marrow cell Fc receptors (FcR II) with monoclonal anti-mouse FcR II antibody inhibits the CL response to IgG2b anti-T cell antibody-coated thymocytes and thus strongly suggests that the stimulation of CLPC oxidative metabolism in this model results from the binding of opsonized T cells to plasma membrane Fc receptors. These observations lend additional support to increasing evidence that the initiation of effector functions by monoclonal anti-T cell antibodies may be strictly dependent upon the presence of monocytes and/or macrophages.     

Regulation of influenza virus-specific cytotoxic T cell responses by monoclonal antibody to a human T cell differentiation antigen

The results in this report indicate that the OKT3 monoclonal antibody, which is specific for a human T cell differentiation antigen present on 90 to 95% of peripheral T cells, can exert several effects that regulate the generation and expression of human influenza virus-immune cytotoxic T lymphocytes (CTL). The OKT3 antibody, but not OKT1 or OKT11 (which bind to all peripheral T cells), is able to inhibit anti-influenza CTL effector cell activity. An F(ab')2 preparation of OKT3 IgG were as effective as whole IgG for the inhibition of CTL effectors, indicating that the inhibitory activity of the antibody was not a function of the Fc portion of the molecule. OKT3 IgG and OKT3 F(ab')2 fragments (but not OKT4, OKT8, or OKI were able to inhibit the generation of anti-influenza CTL. The culture of human lymphoid cells with OKT3 in the presence or absence of influenza virus induced radioresistant cells that could suppress the CTL response of fresh autologous lymphocytes to influenza. These results suggest that T cell functions can be regulated by signals that are initiated by the binding of antibody to cell surface molecules that may not be related to the T cell antigen-specific receptor(s).     

A monoclonal antibody reactive with the human cytotoxic/suppressor T cell subset previously defined by a heteroantiserum termed TH2

A hybridoma-secreting monoclonal antibody was produced from the spleen cells of a mouse immunized with human thymocytes. This hybridoma antibody, termed OKT5, was reactive by indirect immunofluorescence with 80% of human thymocytes but only 20% of peripheral blood T cells. Moreover, OKT5 was unreactive with normal B cells, null cells, and macrophages at any dilution tested. A similar pattern of reactivity was seen with an equine antiserum to human thymocytes termed anti-TH2. Fluorescence-activated cell sorting demonstrated that the OKT5 antibody reactivity on peripheral T cells was restricted to the majority of the previously defined TH2+ subpopulation. In functional studies, the OKT5+ subset, like the TH2+ subset, proliferated well to the mitogen Con A and to alloantigens, and contained cytotoxic effector cells after sensitization in MLC, and suppressor effector cells after activation with Con A. In addition, like the TH2+ T cell, the OKT+ T cell was virtually unresponsive to soluble antigen. Thus, the OKT5 monoclonal antibody is reactive with the cytotoxic/suppressor T cell subset. OKT5 should provide an important probe to assess the status of suppressor cells in human disease.     

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.     

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.     

OKT3 monoclonal antibody induces production of colony-stimulating factor(s) for granulocytes and macrophages in cultures of human T lymphocytes and adherent cells

OKT3 monoclonal antibody (mab) recognizes a membrane antigen associated with the T cell antigen recognition receptor, and is known to be mitogenic and to induce lymphokine production. Our studies demonstrate the ability of OKT3 mab to induce from cultures of human T lymphocytes supplemented with adherent cells the production of colony-stimulating factor(s) for granulocytes and macrophages (GM-CSF) and interferon-gamma (IFN-gamma), an inhibitor of clonal growth of hematopoietic progenitor cells. As has been shown for the mitogenic and IFN-gamma-inducing activity of OKT3 mab, the induction of GM-CSF release in cultures of T cells is strictly dependent on the presence of adherent cells. However, the concentrations of OKT3 mab required for optimal GM-CSF production (50 ng/ml) were found to be 80-fold higher than those sufficient for maximal IFN-gamma production, proliferation, and interleukin 2 production. IFN-gamma activity induced by OKT3 mab partially inhibited colony and cluster formation from progenitor cells of granulocytes and macrophages in vitro. Therefore, neutralization of the IFN-gamma by monoclonal anti-human-IFN-gamma antibody before assay of conditioned medium in bone marrow cultures significantly enhanced the detection of GM-CSF. Kinetic studies demonstrated maximal cumulative GM-CSF production in response to optimal OKT3 mab concentrations on days 4 through 6 in cultures of T cells supplemented with 15% adherent cells. Highly enriched OKT4+ and OKT8+ T cell subsets co-cultured with adherent cells in the presence of OKT3 mab both produced GM-CSF and IFN-gamma and showed similar dose-response curves to OKT3 mab. The requirement for the presence of adherent cells could not be overcome by the addition of purified interleukin 1 or macrophage supernatants. Studies using irreversible inhibitors of DNA (mitomycin C) or protein biosynthesis (emetine-HCl) revealed the necessity of intact DNA synthesis and translation in mononuclear cells to produce GM-CSF in response to OKT3 mab. Loss of GM-CSF production was observed when either adherent cells or T lymphocytes were treated with emetine before co-culture with untreated cells of the other population in the presence of OKT3 mab. In contrast, mitomycin C reduced GM-CSF production significantly when T cells, but not adherent cells, were pretreated. These results suggest that T lymphocytes and adherent cells closely cooperate in the production of GM-CSF induced by OKT3 mab.     

Human T-cell-mediated cytotoxicity: Role of subsets and neutralization of cytotoxicity by anti-α-lymphotoxin serum

T cells were isolated from peripheral blood lymphocytes (PBL) and sensitized to allogeneic PBL in a one-way mixed lymphocyte culture. The sensitized cells were fractionated on the basis of the presence of Fc receptors for IgG (T_G+) or IgM (T_M+), or the absence of both IgG and IgM receptors (T_G?,M?). The Cytotoxicity of the T cells was found to reside principally in the T_G?,M? subset. The degree of target cell lysis by this subset was related to the effector-to-target cell ratio. The sensitized T cells were also separated into subsets by treatment with monoclonal OKT4 antibody and complement (yielding OKT8⁺ cells) or OKT8 antibody and complement (yielding OKT4⁺ cells). The OKT8⁺ subset was the more cytotoxic of the two subsets, and this Cytotoxicity was again related to the effector-to-target cell ratio. The T-cell subsets obtained by these methods were characterized by immunologie and morphologic means. The Cytotoxicity of the total sensitized T-cell population or the T_G?,M? subset could be neutralized to a considerable extent by anti-human α-lymphotoxin (anti-α-LT) serum, and α-LT thus appears to have an important role in cytolysis in this system.     

Modulation induction of the T3 antigen by OKT3 antibody is monocyte dependent

We investigated the influence of monocytes on the susceptibility of the T3 antigen on human T cells to modulation induction by OKT3 antibody. In the absence of monocytes, the T3 antigen was only minimally susceptible to modulation. After the addition of 20% monocytes to the culture, however, complete modulation was readily observed. Furthermore, we found that even in the absence of OKT3 antibody, monocytes were able to down-regulate the expression of the T3 antigen, although to a lesser extent. The ability of monocytes to enhance antigenic modulation proved to be a more general phenomenon. Each individual T cell antigen, however, differed in its susceptibility to modulation by antibody, monocytes, or both, thereby establishing its own characteristic pattern. In addition, after complete modulation of the T3 antigen, the addition of monocytes to the culture thereafter had a distinct inhibitory effect on the reexpression of the T3 antigen. Monocyte enhancement of T3 modulation is significantly reduced when using the OKT3 F(ab')2 fragment, as is OKT3 mitogenesis. After pulsing the monocytes with OKT3 antibody before adding them to the culture, T3 modulation became nearly complete even in the absence of added OKT3 antibody. Monocyte-induced modulation proved not to be MHC restricted, thus allowing for comparative analysis of this effect between monocytes and other cell types. A moderate, however, incomplete modulation enhancement was observed with the human monocyte cell line U937 and with Daudi cells. This finding proved to coincide with the distinct ability of these cell lines to bind OKT3 antibody by their Fc receptors, as was the case with monocytes. In contrast, neither Fc receptor binding nor T3 modulation enhancement was observed with the cell lines Cess and G7. In addition, no effective T3 modulation was observed with glutaraldehyde-fixed monocytes. The overall results seem to indicate that effective modulation of the T3 antigen by OKT3 antibody requires the active participation of Fc receptors on monocytes.     

Distinct classes of human T-cell activation antigens

The characterization of three groups of antigens expressed by activated human T lymphocytes and detected by monoclonal antibodies is reported. Antigens defined by OKT19, OKT21, and OKT22 do not appear on in vitro activated T cells until increases in DNA synthesis become apparent and are not detected on most Interleukin 2 (IL-2)-independent cell lines and normal peripheral blood lymphocytes, monocytes, and granulocytes. Cell surface molecules reactive with the monoclonal antibodies OKT23 and OKT24 are displayed prior to any notable increase in DNA synthesis and are present on IL-2 independent cell lines, irrespective of lineage. T23 and T24 do not appear on peripheral blood cells and their distribution more closely resembles that of the T9 antigen (the receptor for transferrin) than antigens of the other groups. The third group of antigens, T14 and T20, have been classified as "early" antigens relative to DNA synthesis. They are expressed by distinct populations of normal lymphoid cells as well as by some IL-2-independent cell lines. Display of each group of activation antigens on T lymphocytes can be induced by either phytohemagglutinin, purified protein derivative from tuberculin, or allogeneic non-T cells, is not restricted to the OKT4+ or OKT8+ subsets, and is predominant on cells exhibiting the light-scattering properties of blast cells. The relative lack of expression of these antigens among normal peripheral blood cells make them attractive candidates for identifying changes in the status of immune activation.     

Human autologous rosette-forming cells. I. Expression of cell surface antigens in relation to age and lymphoid organ distribution

Autologous rosette-forming cells (auto-RFC) were characterized with monoclonal antibodies to various cell surface antigens using a technique combining immunofluorescence and rosette formation. In peripheral blood, auto-RFC were T cells (Leu 1+/OKT3+) the majority being derived from the helper/inducer subset (Leu 3a+/OKT4+). A small proportion of the circulating auto-RFC were Leu 2a+/OKT8+ and virtually none of them bore T10, T6, and DR antigens or peanut agglutinin (PNA) receptors. In the elderly, the percentages of Leu 3a+ auto-RFC increased significantly along with the augmentation of the Leu 3a+ circulating pool. After Con A stimulation of peripheral blood lymphocytes the autorosette population was expanded and therefore their phenotype was again that of helper cells. In the thymus, high levels of autorosettes are found (30 to 50%). Simple or double labeling of the rosetting cells with various monoclonal antibodies permitted the confirmation of the existence of distinct thymocyte subpopulations and moreover to identify the location of the auto-RFC in the intrathymic differentiation scheme. Nearly 70% of the rosetting cells were derived from common thymocytes, those cells defined by the coexpression of T10, T6, T4, and T8 antigens whether or not they were also stained by OKT3 antibodies. The remaining auto-RFC were found with similar frequency among the T4+ and T8+ mature thymocytes. In the spleen low percentages of auto-RFC were found and the majority resided in the Leu 3a+/OKT4+ population, similarly to peripheral blood autorosettes. Taken together, these data suggest that the expression of autologous erythrocyte receptors is acquired in the thymus and is gradually lost during T-cell maturation.     

Dissection of the role of macrophages in triggering T lymphocytes for interleukin 2 production by monoclonal antibody OKT3

Unfractionated human peripheral blood mononuclear cells produce a small amount of interleukin 2 (IL 2) by stimulation with a monoclonal anti-T3 antibody (OKT3) in vitro. The IL 2 production could be greatly augmented by the addition of a phorbol ester, 12-O-tetradecanoyl-phorbol-13-acetate (TPA). In the presence of TPA, the T cell enriched fraction deprived of macrophages did not produce IL 2, but the T cells pulse-incubated with OKT3 and reconstituted with macrophages efficiently produced IL 2 in subsequent culture in the presence of TPA as did T cells reconstituted with OKT3-pulse-incubated macrophages. The stimulating effect of OKT3 in the presence of macrophages was inhibited dose-dependently by the addition of immunoglobulins, particularly by mouse IgG2a which is the same isotype as that of the OKT3 antibody, showing that it inhibits by blocking the binding of OKT3 to Fc receptors on macrophages. The same extent of IL 2 production was induced in T cells when paraformaldehyde-fixed macrophages were substituted for intact macrophages. Remarkable IL 2 production was also induced by OKT3 when latex beads coated with rabbit anti-mouse IgG2a antibody and TPA were added to the culture. It was confirmed that the production induced by these stimulations was due to an increase of IL 2 mRNA. These results show that effective signals for IL 2 production are generated by efficient crosslinking of T3 molecules which results from multi-interaction of T3 molecules on the T cell membrane and anti-T3 antibody molecules on macrophage membrane or on the surface of the latex particle.     

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

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

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.     

Cellular origin and interactions involved in gamma-interferon production induced by OKt3 monoclonal antibody

OKT3 monoclonal antibody, a human T cell mitogen, induced interferon production by cultured mononuclear cells at 10(-11) M concentrations. Interferon was secreted only under conditions wherein OKT3 was mitogenic, and production was correlated with cell proliferation. Thus, like mitogenesis, interferon secretion reached a peak 3 days after OKT3 stimulation, was inhibited by a factor(s) in human serum, and required 1000 times higher concentrations of Fab and F(ab')2 fragments of OKT3 for induction. The interferon was most likely of "gamma" (immune) type, because pH 2 and 56 degrees C treatments denatured it, whereas anti-alpha or -beta interferon antibodies did not. Mononuclear cells were fractionated into subpopulations that contained OKT4+ cells (helper/inducer T cells), OKT8+ cells (cytotoxic/suppressor T cells), and OKM1+ cells (monocytes) by combining sheep red blood cell rosetting and complement-mediated lysis using monoclonal antibodies against specific cell types. Both OKT4+ and OKT8+ cells proliferated upon OKT3 stimulation with the absolute requirement of OKM1+ cells. However, OKT4+ cells plus OKM1+ cells were necessary for the secretion of interferon. Studies with selective pretreatments with mitomycin C suggested that gamma-interferon was secreted by the OKT4+ cells and that the OKM1+ population subserved an accessory function.     

T cell unresponsiveness to the mitogenic activity of OKT3 antibody results from a deficiency of monocyte Fc gamma receptors for murine IgG2a and inability to cross-link the T3-Ti complex

We recently identified defective monocyte accessory function as the cause of T cell unresponsiveness to the mitogenic activity of OKT3 antibody in cultures of peripheral blood mononuclear cells (PBMC) from five healthy subjects, members of one family. We now report that the underlying abnormality in nonresponders is at the level of monocyte Fc gamma receptors for murine IgG2a. T cell unresponsiveness was not restricted to the signal provided by OKT3 but occurred also for two other anti-T3 antibodies of the IgG2a subclass, in contrast to a normal proliferative response to IgG1 anti-T3 antibodies in one of the OKT3 nonresponders. By using cytofluorography, we found that monocytes from responders but not from nonresponders bound OKT3-FITC to their membrane. The binding could be blocked by mouse IgG2a and by human IgG, but not by mouse IgG1 nor by serum albumin. The data suggest that, through specific Fc gamma receptors for murine IgG2a, monocytes bind the Fc portion of OKT3 during T cell activation. The function of this Fc gamma receptor binding was further studied by culturing PBMC from nonresponders on plates coated with affinity-purified goat anti-mouse IgG antibodies as a substitute for monocyte Fc gamma receptors. The addition of OKT3 to nonresponder PBMC, cultured on such plates, resulted in T cell activation, as evidenced by thymidine incorporation, IL 2 production, and expression of IL 2 receptors. Soluble anti-mouse IgG was not able to substitute for monocyte Fc gamma receptors. The results demonstrate the existence of polymorphism in monocyte Fc gamma receptors for murine IgG2a. They also substantiate that an essential helper function of monocytes in T cell activation by anti-T3 is to provide a matrix for multimeric binding of the Fc portion of the anti-T3 antibodies in order to cross-link T3 molecules.     

Enhancement of murine B cell responses to lipopolysaccharide by supernatants of irradiated peripheral blood leukocytes

Summary At low cell density, the proliferative response of B cells to lipopolysaccharide (LPS) is not detectable. We investigated under these experimental conditions the role of several cell populations on the LPS-induced B-cell proliferation. The addition to murine B cells of irradiated peripheral blood leukocytes (PBL) from the C3H/ HeJ mouse strain, or of culture supernatants of these cells, efficiently restored a response to LPS. Similar results were also obtained with irradiated PBL from other mouse strains and from rabbits. The activities of the culture supernatants were not significantly modified when the PBL were depleted of adherent cells or of Thy-1.2 positive cells, thus suggesting that the active factors were secreted neither by T cells, nor by monocytes.Abbreviations BSS balanced salt solution - ConA concanavalin A - EBMR enhancement of B-cell mitogenic response - J-B, J-T, J-Th, J-MØ, J-PBL, J-RBC splenic bone marrow-derived lymphocytes, splenic thymus-derived lymphocytes, thymocytes, splenic macrophages, peripheral blood leukocytes, red blood cells, obtained from the LPS-non-responding C3H/ HeJ-Pas mouse strain - R-PBL peripheral blood leukocytes obtained from the LPS-responding C3H/ He-Pas mouse strain - LPS lipopolysaccharide - MO macrophages - PBL peripheral blood leukocytes     

Glucocorticoid receptors and corticosensitivity of human thymocytes at discrete stages of intrathymic differentiation

Human thymus is composed of several discrete compartments. Stage III thymocytes, located mainly in the medulla, stain brightly with anti-T3 monoclonal antibody; stage II thymocytes, located in the cortex, are T3- but react with T6 antibodies. The earliest identifiable intrathymic cell (stage I) expresses the sheep erythrocyte glycoprotein T11 but not T6 or T3 antigens. Within the thymus a phenotypically heterogeneous pool of proliferating lymphoblasts is present. This capacity to proliferate without in vitro activation is mainly attributable to thymocytes unable to respond to mitogens and expressing the cortical T6 marker. Both T3+ and T3-T6- cells respond to mitogen. However, in order to exhibit maximal proliferative responses, T3+ but not T3-T6- thymocytes require the addition of exogenous IL 2. Thymocyte subsets at distinct stages of intrathymic differentiation were then analyzed for glucocorticoid (GC) receptor content by using a whole cell assay with 3H-triamcinolone acetonide as tracer. The least mature T3-T6- thymocyte subset contained the highest levels of GC receptors . T3+ thymocytes exhibited a receptor content higher than that found in T6+ cells and similar to that reported for peripheral blood lymphocytes. Apart from the number, the GC receptor sites in all thymocyte subsets were similar in their affinities, kinetic characteristics, specificity for steroids, and ability to undergo translocation from cytoplasm to nucleus, and they behave in all these respects like binding sites of GC receptors in lymphoid and other cells. Independently of both phenotype and GC receptor content, all in vivo activated thymocytes (i.e., spontaneously proliferating cells) were similarly sensitive to the steroid inhibitory action in vitro. Both in the presence and in the absence of exogenous IL 1 or IL 2, the PHA-induced mitogenesis of T3-T6- cells was less inhibited by GC than that of T3+ thymocytes. Exogenous IL 1 and IL 2 were equally effective in removing, although not completely, the GC inhibition on T3-T6- proliferative responses to PHA. Relative to T3+ cell mitogenesis, only exogenous IL 2 was able to antagonize the steroid inhibitory action. The capacity observed in vitro of GC to differentially affect the proliferative potential or the cell viability of thymocytes belonging to functionally distinct subsets suggests that these hormones could regulate the intrathymic maturative pathways. Finally, although at present the physiologic relevance of the highest expression of GC receptors in intrathymic precursor cells remains unclear, the receptor density may be considered a marker of differentiation for the T lymphoid lineage.     

Direct demonstration of binding of anti-Leu 4 antibody to the 40 kDa Fc receptor on monocytes as a prerequisite for anti-Leu 4-induced T cell mitogenesis

It has previously been demonstrated that about 30% of healthy Caucasian subjects are "nonresponders" in assays of the mitogenic activity of monoclonal mouse IgG1 (mIgG1) anti-CD3 antibodies (e.g., anti-Leu 4 and UCHT-1), and that this unresponsiveness is due to lack of monocyte helper function. In an immunofluorescence assay with fluorescence-activated cell sorter analysis, we studied the binding of phycoerythrin-conjugated anti-Leu 4 to monocytes from responders and nonresponders. Interaction was observed with monocytes from responders only, and was blocked by a murine monoclonal antibody (IV.3) directed to an epitope on the 40-kDa low affinity Fc receptor (FcRII). This indicates that the interaction represents binding of the Fc part of phycoerythrin-conjugated anti-Leu 4 to FcRII on responder monocytes. Indirect immunofluorescence with antibody IV.3 demonstrated, however, that monocytes from both responders and nonresponders express similar levels of FcRII. Thus, nonresponder monocytes apparently express a variant FcRII which is unable to bind the Fc part of mIgG1 antibodies. The anti-FcRII antibody completely blocked anti-Leu 4-induced (but not OKT3 (mIgG2a)-induced) T cell proliferation in cultures of peripheral blood mononuclear cells from responders. The results provide direct evidence that monocytes from anti-Leu 4 responders, but not monocytes from anti-Leu 4 non-responders, are able to bind the Fc part of mIgG1 to FcRII, and that this interaction with FcRII is essential for the mitogenic activity of mIgG1 anti-CD3 antibodies.