Chronic giardiasis in B-cell-deficient mice expressing the xid gene

The role of antibody in immunity to Giardia muris infection was investigated by studying B-cell-deficient CBA/N mice expressing the xid gene. After gastric administration of infective G. muris cysts, CBA/N male and female mice developed prolonged G. muris infection, whereas BALB/c mice eliminated their infection in 6 to 8 weeks. Male F1 progeny obtained from matings between female CBA/N mice and male BALB/c mice expressed the xid gene and developed prolonged infections. In contrast, all other F1 progeny of CBA/N and BALB/c matings, which did express the xid gene, eliminated G. muris. The link between the xid gene and prolonged infection was confirmed by studies of C57BL/6 mice congenic for the xid gene. When compared with BALB/c or F1 mice, CBA/N mice produced large quantities of immunoglobulin A (IgA) anti-G. muris antibody in serum and gut secretions during prolonged infection. Serum IgG anti-G. muris antibody levels were reduced in CBA/N and F1 male mice that expressed the xid gene. The inability of xid mice to eliminate G. muris is consistent with the importance of antibody in the development of immunity to G. muris. We hypothesize that mice bearing the xid gene fail to produce IgA antibody of appropriate specificity to an antigen or antigens whose recognition by antibody is critical for successful elimination of the parasite.