Ehigiator, Humphrey Nosayaba.2014-10-2120002000AAINQ57365http://hdl.handle.net/10222/55715In both natural infections and experimental models, the immune response associated with nematode infections is defined by the development of type 2 immune effector pathways. Of these, the increase in reaginic immunoglobulin has received a lot of attention because of its polyclonal nature and the role of such antibodies in allergic responses. However, the mechanisms involved in the development of this unique polyclonal response are still unclear. The focus of this thesis is to investigate the association of the increase in marine IgG1 and IgE, in response to the intestinal nematode Nippostrongylus brasiliensis (Nb), with the induction of Ig isotype switch.To allow for the investigation of this hypothesis both in vivo and in vitro, a reductive approach, involving the use of extracts of Nb, rather than infection, was adopted. The extract was first confirmed to induce a marked increase in IgE and IgG1 levels, similar to that induced by the infection. The extract did not affect the level of IgG2a in serum, showing that the effect was specific to IgE and IgG1 (type 2 associated Ig) rather than inducing a non-specific increase in all Ig isotypes. Assessment of the cytokine profile showed that the extract also induced significant increases in IL-4 and IL-13, both cytokines reported to be involved in the regulation of reaginic Ig isotypes. These results confirm that the extract, like infection, is a strong inducer of polyclonal type-2 responses, and a reliable model for investigating the regulation of nematode induced responses.The extract induced the production of IgG1 when added to in vitro cultures of LPS-stimulated B cells. This provides evidence for the induction of class switch. It did not induce upregulation of IgG1 in naive (unstimulated) B cells, nor expand B cells in in vitro cultures. Analysis of DNA from the spleens of mice treated with the extract by DC-PCR demonstrated a marked increase in the occurrence of reaginic Ig switch region gene recombination in the cells in vivo. These results provide evidence that the marked increase in the Ig response associated with nematode infection is mediated by de novo switch DNA recombination, and not by the expansion of Ig memory B cells.The production of elevated levels of Ig and the inability to induce expansion of B cells suggests that nematodes exert varying modulatory effects on B cell function. This focussed the research on the effects of Nb extract on B cell proliferation. It was found that not only did the extract not induce expansion of naive B cells, it significantly inhibited LPS-mediated B cell proliferation in a dose-dependent manner. The lymphocyte inhibitory effect of the extract was specific to B cells, as proliferation of T cells is not affected. The inhibitory activity does not interfere with early activation events but appears to target signaling pathways downstream of PKC. The inhibitory activity appears to be mediated by modulation of macrophage (accessory cell) activation. The elimination of macrophages from B cell preparations after preactivation appears to render B cells resistant to the anti-proliferative effect of Nb extract upon restimulation in fresh media. Partial characterization of the factor(s) in Nb extract responsible for the inhibitory activity, showed that the factor is a protein with molecular weight of between 50 and 100 kDa.Thesis (Ph.D.)--Dalhousie University (Canada), 2000.Biology, Molecular.Health Sciences, Immunology.text