Intra-articular immunization induces strong systemic immune response in humans.

There is no information available about immunological interactions between the synovial tissue compartment and systemic immunity in health and in disease. The aim of the present study was to evaluate effects of intra-articular immunization on the systemic immune responses in humans. Control subjects were immunized with the same dose of immunogen subcutaneously. Peripheral blood lymphocytes were analysed by spot-ELISA with respect to numbers of immunoglobulin-producing cells and antigen-specific antibody-secreting cells before and 1 week after immunization. Serum and salivary antibody levels were measured by an ELISA before and 14 days after the antigenic exposure. In addition, serum levels of interleukin-6 (IL-6) were analysed before and after immunization. The results indicate that the influenza virus antigen deposited in the joint space induces strong systemic antibody response of IgG, IgA and IgM classes. This response is significantly higher (P less than 0.05) than that of control subjects immunized subcutaneously. In contrast, no significant differences were detected between intra-articularly and subcutaneously immunized subjects with respect to mucosal immune responses. Increased serum levels of IL-6 were observed 1-2 weeks after the vaccination in both experimental groups. We conclude that human joints possess very efficient antigen-presenting properties enhancing systemic B cell reactivity.