A comparison of regional and systemic humoral immune responses to a nematode infection.

The kinetics of humoral immune response against Trichinella spiralis (TS) was characterized with immunofluorescence assay. The mesenteric lymph nodes (MLN) and the spleen of infected rats were examined for concurrent expression of multiple antibody (Ab) isotypes from day 1 to day 15 after infection. The tissues were processed and stained with either a pan-B cell marker (OX33) conjugated with rhodamine (XRITC) or combinations of dual monoclonal Ab probes plus A secondary Ab conjugated with XRITC or fluorescein (FITC). As compared to the uninfected controls, the spleen and the MLN showed significant proliferation of dual-Ab expressing B cells (Debc) on days 5 and 7, respectively. During the immune response, only minimal numbers of B cells expressed single Ab isotype while most B cells expressed more than one isotypes of Ab. When combining all the numbers of Debc within each tissue for each respective days, and comparing those numbers with the total numbers of B cells that were OX33+ in the serial sections of the same tissue specimens, the combined Debc in the spleen were > 6 times higher than the OX33 labeled B cells on day 10, and the Debc in MLN were > 3 times higher than the OX33+ B cells on day 10. Our results thus indicate that the Debc most likely expressed more than two Ab isotypes during the peak days of the humoral immune response to the parasite and this phenomenon occurred in both regional and systemic lymphoid tissues.

Rapidity and multiplicity of synthesis and expression of immunoglobulin isotypes by B lymphocytes in the small intestine.

An immunofluorescence double labeling assay was used to examine the kinetics of intestinal B lymphocytes with concurrent expression of multiple antibody isotypes in the mucosal tissues of rats infected with Trichinella spiralis (TS) muscle larvae for 1 to 15 days. As compared to the uninfected controls (day 0), the non-Peyer's patch tissues of the small intestine contained a significantly increased number of dual antibody-expressing B cells as early as 3 days after infection with a maximum proliferation of these B cells on days 7 and 10. These results indicate the rapidity of B cell response in the small intestine. Similar results were observed in the germinal centers of the Peyer's patches. The non-germinal centers of the Peyer's patch tissues showed delayed kinetics in B cell activation which occurred 10 days after infection. Quantification of the total number of B cells in these tissues was also carried out by staining the CD45RA marker on B cells with the OX33 monoclonal antibody. When comparing the total numbers of B cells with the numbers of B cells expressing dual isotypes of antibodies, our results showed the numbers of dual-expressing B cells (IgA:IgE, IgM:IgE, IgG1:IgE, IgG2a:IgE, IgG2b:IgE, and IgG2c:IgE), when combined, were over 7 times that of the total number of OX33-labeled B cells on day 7 in the small intestine. The dual-expressing B cells in the Peyer's patch-germinal center were more than 5 times that of the OX33-labeled B cells on day 15. These results therefore suggest that the dual-expressing B cells most likely synthesized and expressed more than two isotypes of antibodies during the peak days of the humoral response. Such phenomenon was not observed in non-germinal centers of the Peyer's patch tissues.