Physiological regulation of antigen binding to T cells: role of a soluble macrophage factor and of interferon

Supernatants of human leukocytes contain mediator, different from interferon gamma, which induces expression of MHC class II antigens

In this report, data are presented on the regulation of MHC class II antigen expression by a mediator present in supernatants of human mixed leukocyte cultures (MLC-SN), and which is different from IFN-gamma. The capacity of supernatants to induce antigen expression did not correspond to titers of IFN-gamma. Removal of IFN-gamma using either dialysis against pH 2 or neutralizing mAb against human IFN-gamma did not abrogate the MHC class II antigen expression-inducing capacity of MLC-SN when tested on adenocarcinoma cell lines, kidney epithelial cells, and fibroblasts in vitro in an indirect immunofluorescence assay. Therefore, supernatants of human leukocytes contain a mediator, different from IFN-gamma, which induces expression of MHC class II antigens. Dose-response studies revealed that the mediator is produced after allogeneic and lectin stimulation of human leukocytes, and by unstimulated leukocytes. Activation of leukocytes resulted in increased titers of the mediator. The mediator markedly enhances expression of both HLA-DR and HLA-DQ antigens, whereas IFN-gamma had a similar effect on HLA-DR antigens, and only a minor effect on HLA-DQ antigens. Interaction of the mediator and IFN-gamma resulted in a potentiating effect of these two factors on MHC class II antigen expression. Biochemical analysis revealed a mediator, distinguishable by FPLC from IL-1, IL-2, and human IFN-gamma, and which has a molecular mass of 32 kD.

Induction of lupus inclusions by sera from patients with systemic lupus erythematosus

A sensitive in vitro bioassay for the alpha-interferon induction of lupus-type inclusions (LI) has been established with the human B lymphoblastoid cell line, Daudi. Sera from 11 patients with systemic lupus erythematosus (SLE) were evaluated with this assay. LI induction by these sera increased in proportion to their antiviral activity on Madin-Darby bovine kidney (MDBK) cells. Two of these sera did not induce LI; they showed no antiviral activity on the MDBK cell assay. Clinically and serologically, their donors were in remission. Two sera induced the formation of LI that exceeded the maximum frequencies obtained with 3 alpha-interferon preparations. These sera had the greatest antiviral activities, and their donors had the greatest disease activities. Antisera to alpha-interferons prevented the induction of LI with the pure and homogeneous recombinant human leukocyte interferon, IFLrA, and SLE sera. Together, these results provide evidence that the alpha-interferon endogenous to SLE patients has a great ability to induce LI, and the SLE serum induction of LI corresponds well to the patient's disease activity.

Antigen-binding human T suppressor cells and their association with the HLA-DR locus

The ability of human lymphocytes to bind antigen was studied by direct binding of 125I-labeled streptococcal protein antigen, followed by autoradiography. T-enriched lymphocytes depleted of adherent cells and B cells showed specific binding of 125I-labeled streptococcal antigen (SA) at 4 degrees C and in the presence of sodium azide. Further depletions of the T-enriched population by the monoclonal T4 or T8 antiserum and complement revealed that the antigen-binding T cell is T4-, T8+. This was confirmed by positive selection of T8 cells, by rosetting with ox red blood cells and by the binding of SA by in vitro induced suppressor but not helper cells. Antigen specificity of binding to the suppressor cells was established by complete inhibition with the SA but no inhibition with keyhole limpet hemocyanin. A characteristic dose-response of binding 1 or 10 ng SA to HLA-DRw6 lymphocytes and 1000 ng SA to DR4,1,2,3 or 5 lymphocytes was found. A comparison of the dose-responses of antigen-binding T8+ suppressor cells with those of helper and suppressor functions showed that the dose of SA which binds to suppressor cells is similar to the dose required to induce helper but not suppressor function. A plausible interpretation of these observations is that the T8+ antigen-binding suppressor cells might function as "contrasuppressor cells" which compete successfully for the membrane receptors of helper cells, thereby preventing suppression by the major subset of suppressor cells.

Human interferon-gamma enhances the expression of class I and class II major histocompatibility complex products in neoplastic cells more effectively than interferon-alpha and interferon-beta

Human interferon-gamma was more effective than interferon-beta or -alpha in stimulating production of immunoassociated antigens; HLA-A, -B, and -C; and beta(2)-microglobulin in human M14 and Namalva cells. The comparison was made on the basis of antiviral units, and the stimulation could be abolished by treatment of the interferon-gamma preparation with pH 2 or anti-interferon-gamma serum.

Interferon-dependent induction of mRNA for the major histocompatibility antigens in human fibroblasts and lymphoblastoid cells

In human cells treated with interferons, there is an increase in the amount of HLA-A,B,C and beta 2-microglobulin exposed on the cell surface. We have used a cloned HLA-A,B,C cDNA probe to demonstrate by molecular hybridization that this effect of interferon is preceded by a large increase in the amount of HLA mRNA in the cell. This effect was found in five different human cell lines, with purified leukocyte and fibroblast interferons. The increase in HLA mRNA is comparable in its kinetics and dose-response to the induction of (2'-5') oligo(A) synthetase mRNA by interferons. Therefore, interferons seem to activate at least two cellular genes which have different biochemical functions.

Serum interferon levels in patients with systemic lupus erythematosus

Levels of interferon (IFN) were measured in 81 serum samples from 23 patients with systemic lupus erythematosus (SLE) by a plaque-reduction method and correlated retrospectively with clinical records of disease activity, anti-DNA binding, and serum complement measurements. IFN titers were found to correlate with both clinical disease activity and anti-DNA binding, but no relation was found to serum complement. Most (76.6%, 31 of 41) serum samples obtained during periods of active disease contained measureable amounts of IFN, but only 9.1% (2 of 22) of results of tests on samples obtained during periods of disease quiescence were positive (P less than 0.005). Of samples with clearly elevated anti-DNA binding (greater than 40%), 69.7% (23 of 33) had positive results for IFN, but 57.1% (8 of 14) had negative results when the anti-DNA binding was normal (less than 20%) (P less than 0.005). Measurement of serum IFN titers in patients with SLE, therefore, provides another serologic marker of disease activity. Contrary to the findings of previous studies, the IFN found in the present study was characterized as IFN-alpha, or Type I IFN, on the basis of acid stability and neutralization by antibody to IFN-alpha. Of interest are the questions raised about the origin of IFN in the sera of patients with SLE and what role IFN might have in the pathogenesis of the autoimmune disease in view of the many documented immunomodulating effects of IFN.

Enhancement of Fc gamma receptor expression in interferon-treated mice

Treatment of C3H mice with partially purified or highly purified virus-induced interferon resulted in a marked increase in the expression of Fcgamma receptors (Fcgamma R) on splenic lymphocytes, mesenteric lymph node cells and thymocytes from cortisone-treated mice. An increase on Fcgamma R on splenic lymphocytes was seen as early as 5 h and lasted at least 72 h after a single injection of interferon. We suggest that enhancement of Fcgamma R is one of the mechanisms by which interferon exerts some immunostimulating effects in vivo.

Interferon enhances the amount of membrane-bound beta2-microglobulin and its release from human Burkitt cells

Human leukocytes interferon (HuIFN-A) increased the amount of beta2-microglobulin on the surface of human Burkitt lymphoma cells (Ramos) and also increased the amount released into the culture medium. The effect was observed 1 h after addition of IFN. These results suggest that the increase in beta2-microglobulin on the cell surface of IFN-treated cells is not due to a decreased shedding of antigen from the cell surface, nor an "unmasking" of surface antigen, but rather to an increased synthesis of antigen.

Antigen presentation and regulatory functions of human monocytes in the in vitro response of lymphocytes against purified protein derivative of tuberculin (PPD)

Monocyte functions in the primary and secondary proliferative responses of human lymphocytes against purified protein derivative of tuberculin (PPD) have been studied. By applying the antigens either directly to the responding cells or on antigen-treated autologous monocytes, it was possible to distinguish between two different monocyte functions: antigen presentation and regulation. Their helper function in lymphocyte proliferation was found in cell-free supernatants of autologous and allogeneic monocytes and was expressed better in the secondary rather than in the primary responses. The antigen-presenting function of monocytes, however, was found to be more substantial in the primary response of lymphocytes. These results suggest that macrophage dependency of certain immune functions should be considered in regard to the various functions of macrophages, since at least quantitative differences for each of the macrophage functions were found in the primary and secondary proliferative responses.

Specificity of antigen binding by T cells; competition between soluble and Ia-associated antigen

Competitive antigen binding experiments were performed with purified T and B cells of C3H.SW (H-2b) mice. As antigen, (T,G)-A--L [poly-L(Tyr,Glu)-poly-DL-ALa-poly-L Lys] was used, both in an Ia-containing form, released by adherent cells (IAC-Puri and Lonai, Eur. J. Immunol. 1980. 10:273), and in regular solution. It was found that regular (T,G)-A-L did not compete with the binding of 125I-labeled-IAC-(T,G)-A--L even at a 10(4)-fold excess, whereas IAC-(T,G)-A--L inhibited binding at 10-fold excess. The specificity of (T,G)-A--L binding to high-responder T and B cells was compared by using related branched synthetic copolymers as competitors. B cells cross-reacted with (T,G)-A--L, (H,G)-A--L, (G)-A--L and (T,G)-Pro--L. In contrast, antigen binding C3H.SW T cells cross-reacted only with (T,G)-A--L and (Phe, G)-A--L to both of which they are Ir gene-controlled high responders. Evidence for the Ir gene control of IAC-binding T cells was obtained by showing that high X low responder F1 hybrid T cells preferentally bind IAC-(T,G)-A--L processed by processor cells deriving from the high-responder parental strain. These data are interpreted to suggest that T cells have high affinity for antigen plus self Ia complexes, whereas they have a much lower, if any, affinity for free antigen. It also follows from the results that the structure of the complex ligand may have a role in defining the specificity, H-2 restriction and Ir gene control of T cells.

Regulation of murine macrophage Ia-antigen expression by products of activated spleen cells

This investigation examined the effects of mediators derived form activated spleen cells on macrophage Ia-antigen expression and function. Incubation of adherent thioglycollate-induced murine peritoneal macrophages(> 90% Ia-) with concanavalin A (Con A)-stimulated spleen cell supernate (Con A sup) resulted in a dose-dependent increase in the percentage of Ia-containing (Ia+) phagocytic cells, as detected by antiserum-and-complement-mediated cytotoxicity. The Ia-antigen expression of macrophages incubated with unstimulated spleen cell supernate supplemented with Con A (Control sup) declined. Pretreatment of the macrophages with anti-Ia and complement before addition of the Con A sup did not inhibit subsequent Ia-antigen expression, suggesting that Ia- macropohages were converted to Ia+ cells. These findings were not a result of adsorption of soluble Ia-antigen from the Con A sup, because Ia-antigen expression was detected by an antiserum specific for the haplotype of the macrophages but not that of the allogeneic spleen cells from which the supernate was prepared. Con A sup-cultured macrophages also stimulated the proliferation of allogeneic spleen cells significantly better than Control sup-cultured macrophages in the mixed leukocyte reaction (MLR). Pretreatment of Con A sup-cultured macrophages with anti-Ia and complement before addition of splenic responder cells abrogated their stimulatory capacity, indicating the Ia dependence of the MLR. We hypothesize that regulatory lymphokine(s) can induce both the expression of the Ia+ phenotype by macrophages and the functional capability to stimulate the MLR, and that macrophages lose these capabilities in the absence of such mediator(s).

Antibodies to immunoglobulin heavy chain variable regions protect helper cells from specific suicide by radiolabeled antigen

The antigen-binding receptor of helper T cells was studied by radioactive antigen-caused suicide in vitro. Purified antibodies to immunoglobulin variable regions, obtained from sera of rabbits immunized with isolated VH and VL fragments of mouse myeloma proteins (MOPC 315, XRPC 25), were used to inhibit the binding of radiotoxic antigen. Anti-VH, but not anti-V lambda or anti-V chi inhibited suicide of carrier-primed cells.

Correlated expression of VH framework and VH idiotypic determinants on T helper cells and on functionally undefined T cells binding group A streptococcal carbohydrate

Antibodies to framework determinants of the VH and V lambda fragments of MOPC 315 and antisera to the VH idiotype determinants of the A 5 A antibody were used to analyze the antigen receptors of mouse T (and B) cells. This was done by using the antibodies as inhibitors in (a) an assay in which the binding of radiolabeled streptococcal carbohydrate (A-CHO) antigen by primed and unprimed T and B cells is determined and (b) an assay in which the helper activity of group A streptococcal vaccine-primed T cells is determined. The results suggest that the major proportion of primed and unprimed T cells binding A-CHO (70-90%) exhibit VH framework and VH idiotypic determinants. This population appears to include the helper T cells. A minor proportion of T cells (10-30%) express V lambda-related framework determinants and lack VH framework and VH idiotypic determinants. This population does not include T helper cells. Taken together, the data suggest that a subpopulation of T cells, including the helper cells, uses entire Ig VH regions as part of their antigen receptor system.

The requirement for the expression of previously unexpressed genes in the generation of T and B antigen-binding cells and the changes in sIg isotype following in vitro immunization

The generation of antigen-binding cells (ABC) and plaque-forming cells (PFC) specific for sheep erythrocytes (SRBC) in a primary in vitro response was inhibited by 5-bromo-2′-deoxyuridine (BUdR) present in cultures during the 24 h period immediately preceding harvest. ABC and PFC numbers were greatly reduced by BUdR at a concentration that did not significantly affect cell viability, cell recovery, or the synthesis of total DNA, RNA, or protein, but was sufficient to inhibit the expression of previously unexpressed genes.

The effect of BUdR on ABC was seen no earlier than day 3. It lasted through day 6, with maximum inhibition (80–90%) occurring in the day 3–4 interval, coincident with the peak of the ABC response. PFC were inhibited from day 3 to day 5 (the peak of the PFC response), after which time their sensitivity to BUdR was abruptly lost. ABC were inhibited on days 4, 5, and 6, by as little as 0.5 μg/ml, while on any day, PFC were insensitive to concentrations of BUdR below 2.5 μg/ml. A ten-fold molar excess of thymidine blocked the inhibitory effect of the drug.

Though maximum inhibition of both T and B ABC numbers by BUdR occurred on day 4, its effect on B cells was greater. BUdR had no effect on the numbers of T and B non-antigen-binding cells.

BUdR did not preferentially inhibit surface IgM (sIgM)-bearing ABC though it did prevent the appearance of sIgG receptors on ABC, which normally occurred by day 3, and the loss of sIgD receptors on ABC which was normally complete by day 4. Thus, BUdR decreased the expression of receptors on T ABC as well as B ABC, and prevented the shift in the surface Ig isotypes on B ABC that normally accompanied antigen-driven differentiation.

Selective participation of immunoglobulin V region and major histocompatibility complex products in antigen binding by T cells

Antigen-binding inhibition studies using microscopic autoradiography were performed on T or B cell-enriched lymphocyte populations. Antibodies specific for the "framework" of immunoglobulin heavy or light chain variable domains (VH or VL), or anti-H-2 and anti-Ia antisera were used. T cell subclasses were separated with anti-Lyt antisera and complement. It was found that antigen-binding T cells of different subclasses can be inhibited selectively with only one of the two anti-V region antibodies. Antigen binding to Lyt-1+ cells was inhibited by anti-VH, while Lyt-2+,3+ cells were inhibited by anti-VL specifically. Anti-Ia antisera inhibited unprimed Lyt-1+ antigen-binding cells, whereas anti-H-2K or anti-H-2D anti-sera inhibited unprimed Lyt-2+,3+ antigen-binding cells, and both classes of immune T antigen-binding cells.

Immune mechanisms and the action of interferon in chronic hepatitis B virus infection

Cytotoxic T lymphocytes can eliminate cells infected with hepatitis B virus. A defect of T lymphocyte-mediated cytolysis seems to exist in chronic hepatitis B infection. T cell-mediated lysis is dependent on HLA antigens of the infected host and this may explain the increased or decreased frequency of particular HLA antigens in chronic carriers of hepatitis B virus. This virus may decrease the concentration of HLA antigens expressed on liver cells. Interferon increases the HLA antigen expression on T lymphocytes and hepatocytes, thereby enhancing T lymphocyte-mediate lysis of infected liver cells and elimination of the hepatitis B virus.