EARLY APPEARANCE OF NATURAL MUCOSAL IGA RESPONSES AND GERMINAL-CENTERS IN SUCKLING MICE DEVELOPING IN THE ABSENCE OF MATERNAL ANTIBODIES

We have examined the role of passively transferred maternal Abs in the ontogeny of ''natural'' mucosal IgA responses before weaning of suckl ing mice by comparing the immune status of gut-associated lymphoid tis sue (GALT) (Peyer's patches, mesenteric lymph nodes, and lamina propri a) in 7- to 25-day-old F-1 severe combined immunodeficient (scid)/+ mi ce generated through reciprocal crosses of C.B17 scid/scid and normal congenic (+/+) adult mice. We have also examined the ability of prenat al vs postnatal transfer of maternal immunity to forestall the develop ment of natural neonatal mucosal IgA responses by swapping litters of F-1 scid/+ pups at birth between +/+ and scid/scid mothers. Our result s demonstrate that F-1 scid/+ pups born to or nursed by scid/scid moth ers undergo an accelerated development of natural IgA responses that i nclude germinal center reactions in both Peyer's patches and mesenteri c lymph nodes. These early IgA responses are evident as: 1) increased frequencies of IgA-producing GALT organ cultures; 2) increased mean Ig A output by GALT organ cultures; 3) increased frequencies (>1 log) of IgA-secreting cells from GALT detected by ELlSPOT at 16 days of age; a nd 4) germinal center development by 17 days of age detected by in viv o bromodeoxyuridine incorporation. Finally, FAGS analyses of enteric b acteria isolated from F-1 scid/+ pups and stained for the presence of surface-bound mouse IgA demonstrate that the bacterial flora is a majo r target of both maternal secretory IgA and of the earliest IgA Abs pr oduced in the neonatal GALT of pups deprived of maternal immunity.