Immune responses related to protection against rotavirus after natural infection and vaccination

Abstract

Rotavirus is the most important cause of severe gastroenteritis in children under five years of age and is estimated to be responsible for one-third of all diarrhea-associated hospitalizations and 600,000 deaths/ year worldwide. 1500-1700 rotavirus-associated hospitalizations of children are estimated to occur annually in Sweden (3.7 hospitalization/ 1000 children/y). An effective rotavirus vaccine early in life would have a beneficial effect on child health. Oral vaccine candidates have provided good (63-89%) but not complete protection. The mechanisms and proteins involved in mediating protective immunity are still unresolved.

The role of immunoglobulin A (IgA) in relation to protective immunity was evaluated. A method for purification of human IgA, utilizing the galactose-binding lectin jacalin from the jack-fruit Artrocarpus integrifolia, was used for determination of IgA antibody specificity for different rotavirus proteins and the role of IgA in the neutralization of rotavirus. In convalescent sera from children with an acute rotavirus infection, serum IgA antibodies were detected against VP2, VP4, VP6, VP7, NSP2, and/or NSP3. Serum IgA antibodies purified from rotavirus seropositive individuals were shown in vitro to neutralize unattached and attached rotavirus. A library of monoclonal secretory IgA antibodies directed against the neutralizing antigen, VP4 of rotavirus, were shown to protect mice against rotavirus induced diarrhea and neutralize rotavirus after transcytosis through epithelial cells.

Rotavirus non-structural protein, NSP4, was recently suggested to function as a viral enterotoxin and to play a role in the induction of diarrhea. The ability of rotavirus NSP4 to induce a humoral and cell-mediated immune response was examined. NSP4 stimulated a cell-mediated immune response in naturally exposed adults, and a modest humoral immune response in naturally infected children, vaccinated children (oral RRV-TV), and naturally exposed adults.

Since the oral rotavirus vaccine candidates provide good but not complete protection; the possibility of parenteral immunization with formalin inactivated rotavirus (I-RRV) was evaluated. I-RRV was administered three times intramuscularly to mice and induced a good IgG response, neutralizing antibodies and protective immunity. The two adjuvants tested with a similar immunization schedule, MPL® and monooleate/lauric acid, induced higher IgG antibodies, slightly higher neutralizing antibody titers and protective immunity. The last adjuvant tested, PCPP, induced ~10-fold higher IgG antibody titers and neutralizing antibody titers as well as induced protective immunity after two doses in a dose-dependent manner compared to inactivated virus alone.