Antigen presentation by hapten-specific B lymphocytes. III. Analysis of the immunoglobulin-dependent pathway of antigen presentation to interleukin 1-dependent T lymphocytes

Anergic B cells constitutively present self antigen: enhanced immunoglobulin receptor-mediated presentation of antigenic determinants by B cells is hierarchical

Presentation of hen egg lysozyme (HEL) by HEL-specific B cells was studied in transgenic mice expressing anti-HEL immunoglobulin (Ig-transgenic). In T hybridoma assays, presentation of the HEL46-61 determinant by B cells from Ig-transgenic mice required 10(3)-10(4)-fold lower concentrations of HEL than were required for presentation by B cells from non-transgenic mice. In contrast, presentation of the HEL determinants 112-129 and 25-43 by HEL-specific B cells was either not significantly enhanced, or enhanced only 10-fold compared with B cells from non-transgenic mice. Enhanced presentation of HEL determinants by B cells from Ig-transgenic donors was specific for HEL, since keyhole limpet hemocyanin or synthetic HEL46-61 peptide were presented comparably by B cells from Ig-transgenic mice and non-transgenic littermates. A minimum of 1-4% Ig-transgenic B cells was required to detect enhanced presentation of HEL46-61 in vitro. Constitutive presentation of the HEL46-61 determinant, but not the HEL25-43 or HEL112-129 determinants, was detectable on anergic HEL-specific B cells from double (HEL/Ig)-transgenic mice. In the presence of exogenously added HEL, anergic B cells presented all three HEL determinants. Constitutively presented HEL46-61 was not due to endogenous synthesis of HEL antigen by anergic B cells from double-transgenic mice, as comparable levels of the HEL46-61 determinant were constitutively presented by B cells from Ig-Tg-->HEL-Tg irradiation bone marrow chimeric mice. Firstly, these results indicate that the enhanced antigen presentation mediated by Ig receptors on B cells is not equivalent for all antigenic determinants. Secondly, the data demonstrate that anergic, autoreactive B cells efficiently process and present nominal antigens in addition to constitutively presenting specific self antigen in vivo.

Antigen processing and presentation by small and large B cells

We have investigated the ability of different cells from non-immunized mice of the BALB/c strain to present antigen to two ovalbumin-specific I-Ad-restricted T hybridomas. Lipopolysaccharide-activated B-cell blasts were found to be the most efficient antigen-presenting cells. Purified small and dense splenic B cells also stimulated the hybridomas, although not to the same extent as the activated blasts, but comparable to non-fractionated spleen cells. Glutaraldehyde-treated B cells failed to present antigen, whereas F(ab')2 anti-mouse IgM-treated B cells exhibited markedly increased ability to present antigen. Using flow cytometry, we further purified the resting B cells by sorting the small lymphocytes to ensure that the ability of these cells to activate the hybridomas was not due to contamination with large non-resting B cells. The sorted small B cells retained the ability of antigen presentation. Their resting state was confirmed by the fact that they did not incorporate [3H]-thymidine as shown by autoradiographic analysis.

Induction of human IgE synthesis by CD4+ T cell clones. Requirement for interleukin 4 and low molecular weight B cell growth factor

We have analyzed in detail the precise requirements for the induction of human IgE synthesis using several experimental approaches with purified B cells and well-characterized alloantigen-specific CD4+ T cell clones expressing different profiles of lymphokine secretion. Using these clones under cognate conditions in which the B cells expressed alloantigens recognized by the cloned T cells, we have confirmed that IL-4 is required for the induction of IgE synthesis, but we have clearly demonstrated that IL-4 by itself is not sufficient. With several cloned CD4+ T cell lines, including an IL-4-producing clone that could not induce IgE synthesis, and cloned T cells pretreated with cyclosporin A to inhibit lymphokine synthesis, we showed that Th cell-B cell interactions are necessary for IgE synthesis, and that low molecular weight B cell growth factor (LMW-BCGF) and IL-4, in combination, are lymphokines of major importance in the induction of IgE synthesis. Together our results indicate that optimal induction of an IgE-specific response requires the exposure of B cells to a particular complex of signals that include (a) a signal(s) involving Th-B cell interaction that primes B cells to receive additional signals from soluble lymphokines, (b) a specific B cell proliferative signal provided by LMW-BCGF, and (c) a specific B cell differentiation signal provided by IL-4.

Regulation of T-cell activation: differences among T-cell subsets

Four regulatory phenomena appear to regulate differentially the activation of TH1, TH2, and CTL clones. First, IFN-gamma selectively inhibits proliferation of TH2 but not TH1 cells; lymphokine production by TH2 cells is not affected by IFN-gamma. In addition, when fresh OVA-specific HTL clones are derived in the presence of rIL-2 TH2 cells are preferentially obtained, whereas TH1 cells predominate if cloning is performed in rIL-2 plus rIFN-gamma. These results suggest that the presence of IFN-gamma during the course of an immune response would result in the preferential expansion of HTL of the TH1 phenotype. Proliferation of CTL clones is not influenced by IFN-gamma. Second, different APC populations appear to differentially activate TH1 and TH2 clones. Purified splenic B cells stimulate optimal proliferation of TH2 but not TH1 cells, whereas macrophage/dendritic cells appear to stimulate optimal proliferation of TH1 but not TH2 cells. Since both APC types stimulate lymphokine production by each of the HTL subsets, these results suggest the existence of TH1- and TH2-specific cofactors for growth. Third, high doses of immobilized anti-CD3 mAb inhibit IL-2-dependent proliferation of TH1 but not TH2 clones. Since this effect appears to require calcium, this observation suggests that TCR-mediated signalling events might differ between the two HTL subsets. Indeed, little or no increase in [Ca++]i can be detected in TH2 clones stimulated with Con-A, while such an increase is easily discernible in TH1 cells. Although high concentrations of immobilized anti-CD3 mAb inhibit IL-2-dependent proliferation of CTL clones, proliferation of these cells in response to immobilized anti-CD3 alone reaches a plateau. Since activation with anti-CD3 is thought to mimic antigenic stimulation, these results suggest that antigen concentration may play a role in determining which predominant T-cell types proliferate in a particular immunological situation. Fourth, pretreatment of TH1 cells, but not TH2 cells or CTL, with IL-2 results in decreased lymphokine production and proliferation in response to subsequent stimulation via the TCR. This antigen-responsive state appears to involve a defect in calcium-dependent signalling, providing additional evidence for different signalling mechanisms in TH1 and TH2 clones.(ABSTRACT TRUNCATED AT 400 WORDS)

Synthesis of interleukin-1-like activity by normal rat chondrocytes in culture

Chondrocytes prepared from the articular cartilage of young rats synthesize and secrete an interleukin-1-like activity into the medium. The physical and biochemical properties of this IL-1-like activity are similar to macrophage-derived IL-1. Immunological studies suggest that this activity is related to IL-1 alpha. Isolated chondrocytes and those grown in culture can express Ia.

Heterogeneity of helper/inducer T lymphocytes. I. Lymphokine production and lymphokine responsiveness

Antigen-specific, Ia-restricted helper/inducer T lymphocytes consist of subsets that can be distinguished by lymphokine secretion. One, called Th1, secretes IL-2 and the other, termed Th2, produces BSF-1/IL-4 in response to stimulation by lectin or antigen receptor signals, and each uses the respective lymphokine as its autocrine growth factor. Cloned lines representing Th2 cells proliferate in response to both IL-2 and their autocrine lymphokine, BSF-1/IL-4, but this proliferation is dependent on the synergistic costimulator activity of the monokine, IL-1. In contrast, Th1 clones proliferate only in response to IL-2, are unresponsive to BSF-1/IL-4, and their growth is unaffected by IL-1. These response patterns are not attributable to variations in culture conditions but apparently reflect intrinsic properties of the two T cell subsets. Moreover, the unresponsiveness of Th1 cells to BSF-1/IL-4 may be related to lower levels of expression of surface receptors for this lymphokine. These results may explain the observed heterogeneity among bulk populations of T cells in terms of lymphokine responsiveness and requirement for accessory factors (costimulators). In addition, our findings suggest that IL-2, unlike BSF-1/IL-4, is a fully competent growth factor that is potentially involved in antigen-independent expansion of bystander T cells present at sites of immune stimulation.

The basis for the immunoregulatory role of macrophages and other accessory cells

Macrophages handle extracellular proteins and secrete diverse bioactive molecules and, therefore, influence the physiology of many tissues. They also have an important immunoregulatory role. The immune response to proteins involves the activation of the T helper subset of lymphocytes. The T helper cell is activated only when it interacts with the protein displayed on the surface of a macrophage or other accessory cell. This interaction involves restrictive proteins encoded in the major histocompatibility gene complex as well as growth-differentiating proteins.