Evidence of thymus-independent local and systemic antibody responses to Cryptosporidium parvum infection in nude mice

Differences in susceptibility to persistent cryptosporidial infection betwe en two strains of adult athymic nude mice prompted us to investigate the im mune mechanism(s) that may control resistance to infection in these T-cell- deficient mice. We studied fecal oocyst shedding, serum and fecal parasite- specific antibody responses, and fecal immunoglobulin levels in athymic C57 BL/6J nude and athymic BALB/cJ nude mice following oral inoculation with Cr yptosporidium parvum oocysts at 8 to 9 weeks of age. C57BL/6J nude mice had significantly higher fecal parasite-specific immunoglobulin A (IgA) (days 27, 31, 35, and 42 postinoculation) and IgM (days 10, 17, 24, 28, 31, 38, 4 2, and 48 postinoculation) levels than BALB/cJ nude mice (P < 0.05) and sig nificantly higher serum parasite-specific IgA levels at 63 days postinocula tion (P < 0.03). Moreover, C57BL/6J nude mice shed significantly fewer C. p arvum oocysts than BALB/cJ nude mice from days 52 to 63 postinoculation (P < 0.05). In contrast, BALB/cJ nude mice had higher levels of non-parasite-s pecific IgA (days 38 to 63 postinoculation) and IgM (days 24, 35, 38, and 5 2 postinoculation) than C57BL/6J nude mice in feces (P < 0.05). These data suggest that parasite-specific fecal antibodies may be associated with resi stance to C. parvum in C57BL/6J nude mice.