Regional differences of B cell immune responses to (4-hydroxy-3 nitrophenylacetyl) acetic acid (NP) antigen in senescent mucosal immune system.

The age-associated primary immune response of B cells from the mesenteric lymph nodes (MLN), the bronchial lymph nodes (BLN), lamina propria (LP), Peyer's patches (PP), and the spleen (Sp) of mice following peritoneal or oral immunization with (4-hydroxy-3-nitrophenylacetyl) acetic acid (NP) conjugated bovine gamma-globulin (NP-BGG) was investigated. The induction of immune responses was assessed in 4-, 11-, and 24-month old individual C57BL/6J male mice by determining the number and isotype of anti-NP ELISPOT-forming cells (SFC) in the MLN, BLN, PP, LP, and Sp, and the titer and isotype of serum anti-NP antibody. Data indicated a significant age-associated decline in immunoglobulin M (IgM) and IgG anti-NP SFC in the Sp. No age-related declines were seen in the anti-NP SFC responses in the MLN and BLN. Oral immunization of mice with soluble NP-BGG in combination with cholera toxin resulted in anti-NP SFC responses in LP and PP, which were predominantly of the IgM class followed by IgG and IgA. There were age-associated increases in IgM, IgG, and IgA anti-NP SFC responses in the LP and PP with negligible responses in the SP and MLN. Serum anti-NP IgM and IgG antibody titers in mice immunized intraperitoneally with NP-BGG were found to decline with age. Isoelectric focusing and affinity immunoblotting revealed a loss of several anti-NP antibody clonotypes in the immune serum of old mice following parenteral immunization with NP-BGG as opposed to several new antibody clonotypes following oral immunization. The findings suggested age-related regional differences of B cell immune responses to the NP antigen in the mucosal immune system. These changes in the NP specific antibody repertoires in the spleen and mucosa-associated tissues may be regulated by different mechanisms operating towards different antigens, and this in turn may influence the characteristic antibody responding to these antigens.