Analysis of homotypic and heterotypic serum immune responses to rotavirus proteins following primary rotavirus infection by using the radioimmunoprecipitation technique

Three sequential serum samples collected from each of 20 young children with a naturally acquired primary rotavirus infection were assayed by the radioimmunoprecipitation technique for immunoglobulin G antibodies to rotavirus structural and nonstructural proteins of the four major human rotavirus serotypes G1, P1A; G2, P1B; G3, P2; and G4, P2. Fourteen children were infected with a serotype G1 rotavirus strain and six children were infected with a serotype G4 rotavirus strain. Sera were collected from each child in the acute and convalescent periods postinfection and also approximately 4 months later. Serum immune responses to rotavirus core antigens VP2 and VP3, to the major inner capsid antigen VP6, to nonstructural proteins NS35, NS28, and NS26, and to the outer capsid neutralization antigen VP4 of all test strains were detected in the majority of patients. These responses do not appear to be influenced by the G type or P type of the rotavirus strain used in the reactions. Homologous responses to the main neutralization antigen VP7 were detected in 93% of patients with serotype G1 infections and 50% of patients with serotype G4 infections. Heterologous VP7 responses were less frequently detected and were restricted to G1, G3, and G4 serotype rotavirus strains. No responses to VP7 of the serotype G2 rotavirus strain were detected in any patients. Heterotypic immune responses to the neutralization antigens, at least following serotype G1 and G4 infections, therefore appear to consist primarily of responses to VP4 rather than to VP7.