Rectal immunization of mice with hepatitis A vaccine induces stronger systemic and local immune responses than parenteral immunization.

Systemic (spleen cell (SPLC), serum antibodies) and intestinal mucosal (Peyer's patch cells (PPC), lamina propria lymphocytes (LPLs), coproantibodies) immune responses were compared in mice immunized with varying doses (144, 72, 36, 18 ELISA units [EU]) of HAVRIX, an alum-adsorbed killed hepatitis A virus (HAV) vaccine, delivered either intrarectally (i.r.) or intraperitoneally (i.p.) in three doses at weekly intervals. HAV-specific IgG, IgM, and IgA antibody responses were evaluated by ELISPOT and EIA and HAV-responsive lymphocytes by lymphocyte stimulation assays. Systemic IgG responses were greater in mice immunized intraperitoneally with 144, 72, and 36EU of HAVRIX, while IgM and IgA responses were greater in PPC and LPL cell populations, serum and coproantibodies of rectally immunized mice, particularly at HAVRIX doses of 36 and 18EU. Rectal immunization at lower doses (36, 18EU) also elicited strong cellular responses in all cell populations while parenteral (i.p.) vaccination, did not. Results suggest that rectal immunization may be a highly effective way of inducing both local and systemic immunity to HAV.