Streptococcal pneumoniae polysaccharide increases IgA-class antibody activity under the immunological memory of a protein antigen: two signals on experimental IgA nephropathy

We designed the following experiment in order to clarify the factors that induce a hyper-immune state of IgA. Six-week-old Balb/c mice were immunized with bovine gammaglobulin (BGG) at 0 and 2 weeks, followed by the administration of phosphorylcholine-BGG (PC-BGG) at 3 and 5 weeks to obtain an immunological memory. At 6 weeks, we divided the mice into three groups: one was a saline group used as a control, another was a PC-BGG group used to investigate T-cell dependent antigen, and the last was a streptococcal pneumoniae polysaccharide (R36A) group used to investigate T-cell independent antigen. We compared the antibody activity in response to BGG, and glomerular immune deposition among the groups. In the control group, antibody activities did not change, and all stainings on glomerular immune deposits were negative. In the PC-BGG group, IgG-class antibody activity was significantly suppressed (p < 0.05), but IgA- and IgM-class antibodies were not affected. The intensity of glomerular deposition of IgM was level one positivity (TFS: 116.7 +/- 20.2 (mean +/- SD)). In the R36A group, polysaccharide produced significant increases (almost four times) in IgA-class and IgM-class antibody activity under the condition of immunological memory (IgA: p < 0.05, IgM: p < 0.005). The intensity of IgA was between weak and level one positivity (TFS: 60.8 +/- 6.3), but the intensity of IgM was weak positive (TFS: 36.7 +/- 10.4). This became a predominant glomerular deposition of IgA in the R36A group.(ABSTRACT TRUNCATED AT 250 WORDS)