Enhancement of in vitro and in vivo antigen-specific antibody responses by interleukin 11.

The availability of large quantities of highly purified recombinant interleukin 11 (rhuIL-11) has allowed us to investigate the effects of rhuIL-11 on sheep red blood cell (SRBC)-specific antibody responses in the murine system. The results showed that rhuIL-11 was effective in enhancing the generation of mouse spleen SRBC-specific plaque-forming cells (PFC) in the in vitro cell culture system in a dose-dependent manner. These effects of rhuIL-11 were abrogated completely by the addition of anti-rhuIL-11 antibody, but not by the addition of preimmunized rabbit serum. Cell-depletion studies revealed that L3T4 (CD4)+ T cells, but not Lyt-2 (CD8)+ T cells, are required in the rhuIL-11-stimulated augmentation of SRBC-specific antibody responses. The effects of rhuIL-11 on the SRBC-specific antibody responses in vivo were also examined. RhuIL-11 administration to normal C3H/HeJ mice resulted in a dose-dependent increase in the number of spleen SRBC-specific PFC as well as serum SRBC-specific antibody titer in both the primary and secondary immune responses. In mice immunosuppressed by cyclophosphamide treatment, rhuIL-11 administration significantly augmented the number of spleen SRBC-specific PFC as well as serum SRBC-specific antibody titer when compared with the cyclophosphamide-treated mice without IL-11 treatment. These results demonstrated that IL-11 is a novel cytokine involved in modulating antigen-specific antibody responses in vitro as well as in vivo.

Enhanced expression of high-affinity interleukin-2 receptors in scleroderma: possible role for IL-6.

Scleroderma (systemic sclerosis) is characterized by tissue fibrosis, a distinctive vascular and microvascular disorder, and a perivascular mononuclear cell infiltration of involved organs. The pathogenesis of scleroderma is not known; however, there is evidence for a cell-mediated immune mechanism in the disease. Enhanced IL-2 production has been documented both in vivo and in vitro. In this study, the effect of IL-2 on lymphocyte proliferation in vitro was examined. An enhanced proliferative response to IL-2 was seen in scleroderma lymphocytes over that in matched control lymphocytes. Since high-affinity IL-2 receptors (HIL-2-R) mediate the growth-promoting activity of IL-2, we examined HIL-2-R expression on lymphocytes from 13 scleroderma and 11 matched control subjects by a radioiodinated IL-2 binding assay. Significantly higher numbers of HIL-2-R were noted in scleroderma cells (3054 +/- 618 in scleroderma vs 1721 +/- 181 in control cells, mean +/- SD; P less than 0.001). The addition of IL-6 to control cell cultures 24 hr prior to binding determination led to changes in IL-2 binding that were identical to scleroderma cell binding characteristics, while the addition of neutralizing IL-6 antibody to scleroderma cells led to a reduction in HIL-2-R expression. Other cytokines (IL-1, IL-3, IL-4, IL-5, TNF, LT, IFN-gamma, and TGF-beta) had no effect on IL-2 binding, suggesting that IL-6 may mediate the enhanced expression of HIL-2-R. This conclusion was further supported by the finding that scleroderma lymphocytes released in vitro 10- to 20-fold higher concentrations of IL-6 than control cells. The data demonstrate an amplification of IL-2 binding in scleroderma and suggest IL-6 as the mediator of this phenomenon.

Characterization of IL-6 production by B cells.

IL-6 production by antigen-specific and antigen-non-specific B cells was studied. It was found that low concentrations of antigen (0.001 micrograms/ml) could stimulate IL-6 production by antigen-specific B cells (10(3)-10(4) fold lower concentration of antigen when compared with that of antigen-nonspecific B cells). A kinetic study showed that IL-6 activity in supernatants from antigen-specific B cells was detectable as early as 2 hours. The production of IL-6 by non-specific B cells and by monocytes was distinctly different. These results suggest that antigen-specific B cells may play a critical role in early T cell activation by antigen.

[Antigen presentation of human B lymphocytes on BCG particulate antigen].

The possibility of human B lymphocytes to process and present BCG particulate antigen to BCG specific T cell line was studied. It was found that about 6% of B cells after incubated with BCG for 24 h, showed BCG bacilli in their cytoplasm, by acid fast stain, and became obscure 48 h later. These results demonstrated that human B lymphocytes could phagocytose, process, and degrade BCG particulate antigen. The BCG pulsed B cells acted as antigen presenting cells to BCG specific T cell line. The proliferation and IL-2 production of specific T cell line were significantly enhanced by BCG pulsed B cell stimulation. It was evident that BCG antigen was presented to T cell lines by B cell. The activity of BCG pulsed B cell was time depending. By treating B lymphocytes with chloroquine which interferes with normal lysosome functions could completely inhibit the proliferation of BCG specific T cell line when B lymphocytes were pulsed with BCG or express of BCG. The results revealed that B cells must process antigen before presenting antigen to T cells. It is concluded that B lymphocytes can phagocytose, process and present relevant determinants of BCG particulate antigen to BCG specific T cell line, and that human B lymphocytes may play an important role in the anti-tuberculous immunity in vivo, at least as antigen presenting cells. To pursue the study of this problem, it is suggested to use B lymphocytes deficient mice as experimental models for further investigation.

[Role of B cell surface IgM in antigen presentation].

Previous studies showed that both resting and lipopolysaccharide activated B cells were very effective accessory cells and antigen presenting cells in T cell responding to mitogens and antigens. This paper discusses the role of B cell surface IgM in antigen presentation. Splenic B cells obtained from C57BL/6 mouse were depleted of macrophages, dendritic cells and T cells. The purified B cells were prepulsed with sheep anti-mouse IgM antibody (SaM) at 4 degrees C for 60 min or with tetanus toxoid antigen (TT-Ag) at 37 degrees C for 12 h before pulsing with TT-Ag or SaM. Then B cells (2 x 10(5)/well) were used as antigen presenting cells without further addition of TT-Ag in TT-Ag primed T cells (2 x 10(5)/well, obtained from TT-Ag immunized C57BL/6 mouse lymph node) proliferation. The results showed that antigen presentation of B cells prepulsed with SaM before pulsing with TT-Ag was blocked. But if B cells were preincubated with TT-Ag before pulsing with SaM, antigen presentation of B cells was not blocked by SaM. These results have suggested that B cell surface IgM can take up antigen and can present the antigen to antigen specific T cells. It has also been revealed that B cell surface IgM by taking up antigen plays an important role in antigen presentation. Also, the biological significance of the role on B cell surface IgM in antigen presentation is discussed.