Previously, a total of 18 adult volunteers was given orally 1 ml of a 0.2% stool filtrate containing the virulent human rotavirus strain D (G1, P1A8, NSP4B) (Kapikian, et al., 1983. J. Infec. Dis. 147:95). Four of 5 who shed rotavirus after challenge developed diarrhea. In an attempt to identify correlates of resistance to rotaviral diarrheal disease and/or infection, we analyzed serum IgA and IgG antibody titers in 16 of the 18 volunteers. We used an immunocytochemistry assay involving a total of 18 different recombinant baculoviruses expressing each of the following major serotype/genotype sepcificities of rotavirus proteins for the serologic assays: VP4 (P8; P4; P6; P9; P10); VP7 (G1-4, G9); NSP4 (A-D); as well as VP6 and NSP2. The prechallenge IgG antibody titers to types G1 and G3 VP7, types P8 and P6 VP4 and type A NSP4 in the non-infected group were significantly higher than those in the asymptomatically infected and symptomatically infected groups. Logistic regression analysis showed that the higher probability of resistance to asymptomatic and symptomatic rotavirus infection correlated with higher prechallenge IgG antibody titers to the homotypic VP7 (G1) (p is equal to 0.0077 for asymptomatic infection; p is equal to 0.0004 for symptomatic infection) and the homotypic VP4 (P8) (p is equal to 0.0091 for asymptomatic infection; p is equal to 0.0011 for symptomatic infection), suggesting that protection against rotavirus infection and disease may be VP7- and/or VP4-homotypic although they may not be the sole determinants of protective immunity.? ? Using an immunocytochemical staining assay involving six different recombinant baculoviruses with each expressing one of the major bovine rotavirus VP7 (G6, G8 or G10) and VP4 (P1, P5 or P11) serotypes, we analyzed IgG antibody responses to individual proteins in archival serum samples collected from 31 Holstein calves approximately monthly from 1 month to 12 months of age during 1974-1975 at the Arizona Dairy Company located in Higley, Arizona. The calves were given colostrum immediately after birth and raised separately from their mothers. The serum samples sent to NIH were stored in a -20 degree Celsius freezer until testing. A total of 309 serum samples were analyzed in this study. Each of 31 calves experienced at least one rotavirus infection as determined by a 4-fold or greater G- and/or P-serotype-specific antibody response during the period of 12 months. Of note was the finding that calves that experienced their first seroresponse between 2 and <4 months of age had a significantly lower antibody titer to certain serotypes at 1 month of age than those that developed a seroresponse later, suggesting that maternal antibody might play a role in delaying primary infections and/or the development of antibody responses. Seroresponses to VP7 and VP4, as determined by a 4-fold or greater antibody response, were not always elicited concurrently following infection: in some calves seroresponses to VP7 were detected earlier than to VP4 or vice versa. In addition, in some calves, a subsequent 2nd seroresponse was detected for VP7 or VP4 only. This temporal dissociation of VP7-VP4 responses may be a function of preexisting maternally-derived or primary infection-induced G and/or P type-specific antibodies in calves present at the time of the 2nd rotavirus infection. Analyses of serum samples showed that the G8 serotype infected calves most frequently (35.5%) followed by G6 (19.4%), G10 (12.9%), and mixed G type infections (32.3%). With regard to VP4, an IgG response to P1 was detected in 25.8% of samples followed by P5 (12.9%), P11 (6.5%), and mixed P type infections (54.8%). The most frequent G-P combination was G8:P1 followed by G8:P5, G8:P11 and G6:P1. Our analyses of VP7- and VP4-specific antibody responses in calves indicated that (i) repeated infections were less likely to be caused by the G and/or P types than those caused by primary infections (Chi square is equal to 3.96, p is equal to 0.047); and (ii) protection against rotavirus reinfection tended to be serotype specific. Although there is still considerable disagreement on the role and importance of serotype-specific immunity in protection against rotavirus-caused illness, our data support the strategy of the administration of a multivalent vaccine and multiple vaccinations in order to elicit broader protection against prevailing serotypes in humans.
