Effects of maternal antibodies on protection and development of antibody responses to human rotavirus in gnotobiotic pigs

Although maternal antibodies can protect against infectious disease in infa ncy, they can also suppress active immune responses. The effects of circula ting maternal antibodies, with and without colostrum and milk antibodies, o n passive protection and active immunity to human rotavirus (HRV) were exam ined in gnotobiotic pigs, Pigs received intraperitoneal injections of high- titer serum (immune pigs [groups 1 and 2]) from immunized sows, low-titer s erum from naturally infected sows (control pigs [groups 3 and 4]), or no se rum (group 5). Immune or control colostrum and milk were added to the diet of groups 2 and 4, respectively. After inoculation (3 to 5 days of age) and challenge (postinoculation day [PID] 21) with virulent HRV, the effects of maternal antibodies on protection (from diarrhea and virus shedding), and on active antibody responses (measured by quantitation of antibody-secretin g cells [ASC] in intestinal and systemic lymphoid tissues by ELISPOT) were evaluated. Groups 1 and 2 had significantly less diarrhea and virus sheddin g after inoculation but higher rates of diarrhea and virus shedding after c hallenge than did groups 3 and 5, Group I and 2 pigs had significantly fewe r immunoglobulin A (IgA) ASC in intestinal tissues at PID tl and at postcha llenge day (PCD) 7 compared to group 5, Significantly fewer Ige ASC were pr esent in the intestines of group 2 pigs at PID 21 and PCD 7 compared to gro up 5. There was a trend towards fewer ASC in intestinal tissues of group 2 than group 1, from PID 21 on, with significantly fewer IgA ASC at PCD 7, Ig G ASC in the duodenum and mesenteric lymph nodes of group 3 and 4 pigs were significantly fewer than in group 5 at PCD 7. These decreases in ASC empha size the role of passive antibodies in impairing induction of ASC rather th an in merely suppressing the function of differentiated B cells. To be succ essful, vaccines intended for populations with high titers of maternal anti bodies (infants in developing countries) may require higher titers of virus , multiple doses, or improved delivery systems, such as the use of microenc apsulation or immune stimulating complexes, to overcome the suppressive eff ects of maternal antibodies.