9406671 Dintzis The goal of this research is to study the mechanism(s) by which soluble arrays of antigen (antigen-arrays) interact with cell surface immunoglobulin receptors (sIg) to induce either cell activation or cell death. The experimental model for these studies is the humoral immune response, wherein B cells with antigen specific sIg either proliferate and differentiate into antibody-secreting plasma cells, or are functionally eliminated, depending on molecular size and hapten valence of the antigen arrays. Previous work from this laboratory has demonstrated profound suppression of specific antibody production in vivo. Ongoing, high level T-cell dependent anti-fluorescein (anti-Fl) IgM, IgG and IgE serum antibodies were reduced 90-99% in adult mice by intraperitoneal administration of fluoresceinated dextran (Fl-Dex) of molecular mass less than 100 kDa. Recent studies with Fl-Dex of molecular mass 30 kDa demonstrated that high affinity anti-Fl antibodies are preferentially eliminated. In contrast, high molecular weight (500 kDa) antigen-arrays are stimulatory at comparable hapten concentrations. Using adoptive transfer experiments, it was shown that suppression is dependent on antigen-array dose and exposure time in the donor animals and can not be attributed to antigen carryover. The suppression affects the B-cell compartment selectively, as carrier-specific T-cell help remains intact and splenic T cells from suppressed mice could not transfer suppression. The molecular basis of the observed suppression is currently being investigated using the anti-nitrophenyl (NP) response as a model system. The anti-NP response in C57BL/6 mice is characterized by a highly restricted VH gene usage as well as a common somatic hypermutation pattern of higher affinity anti-NP memory B cells. Preliminary PCR analysis indicates that memory B cells with the most common somatic hypermutation are eliminated from immunized animals by administration of antigen-arrays. The ma in goal of this project is to test the hypothesis that the elimination of anti-NP memory B cells is the underlying mechanism of suppression. For this purpose PCR analysis will be optimized, quantitative Southern blot analysis employed and the cloned VH amplification products from DNA isolated from NP hyperimmune and suppressed animals will be sequenced. The effect of antigen-arrays on a homogeneous B cell population has been examined in mice transgenic for a phosphocholine (PC)-specific mu heavy chain. Preliminary results indicate induction of apoptosis in these cells by PC-Dex of molecular mass 30 kDa. This experimental system will be used as a model for exploratory studies of the regulation of suppression. Together, these findings indicate that, depending on the physical- chemical characteristics of a multivalent ligand, interaction with B cell surface Ig may result either in positive signaling (cell proliferation and differentiation) or negative signaling (cell death). The ability to induce deliberately, either stimulatory or suppressive signals in B cells by manipulation of the molecular properties of the antigenic material can be used as a tool for the study of the control of cellular function by extracellular multivalent ligand interacting with cell surface receptors. %%% The mammalian immune response is highly regulated. An immune response is started when a foreign substance (antigen) binds to a specific receptor on the surface of a cell of the immune system. It is well known, however, that some antigens may either stimulate an immune response or suppress an immune response, depending on the form in which they are administered and on other factors not well understood. A better understanding of the molecular mechanisms that determine whether a particular signal will result in stimulation or suppression of would be a major contribution not only to our understanding of the regulation of immune function, but would enhance our knowledge more generally of the mec hanisms by which cells respond to external signals. These investigators have preliminary data suggesting that antigens closely related chemically may stimulate or suppress an immune response depending on certain defined physical-chemical properties. The goal of this research is to define more closely the mechanisms by which differences in the molecular properties of an antigenic material lead to dramatic differences in its effect. The ability to induce deliberately, either stimulatory or suppressive signals in cells by manipulation of the molecular properties of signal molecules can be used as a tool for the more general study of the control of cellular function by extracellular signals interacting with cell surface receptors. ***
