[Mechanisms involved in the prolonged humoral immune response: behavior of aphthous fever virus]

Foot and mouth disease (FMD) is a widespread infectious disease affecting cloven-hoofed animals with severe economic consequences. Animals infected with FMD virus (FMDV) develop an immunological status of immunity characterized by high titers of virus serotype-specific neutralizing antibodies (NAb) which persist for at least 18 months. In contrast, currently inactivated virus vaccines elicit lower antibody response for shorter periods. Protection against FMDV infection has been commonly related to the level of NAb in serum. The new generation vaccines are immunologically poor, and for this reason it is important that the immunological mechanisms are activated during the infection to potentiate the action of these vaccines. The objective of this review is to present the possible mechanisms involved in the long lasting humoral immune response after FMDV infection. The necessity of the Ag for the initiation of the response is well known, although its role in maintaining and regulating the immune response is still unclear. The continuous role of the Ag in maintaining the response was demonstrated in experiments in which Abs with different specificities for long periods of time without the administration of exogen Ag were detected. The capture and retention of Ab-Ag complex by dendritic follicular cells seems to be a important factor in the increase of the Ag production and in the generation of B memory cells. The genomic persistence is strongly related to the Ag persistence. During a persistent infection, in which the genome is maintained and able to synthesize proteins, the immune system would be continuously stimulated. The continuous liberation of soluble Ag, as a productive persistent infection, induces the B cells memory for its differentiation in Abs producing cells. The antigen presenting cells (APC) are cells which present the Ag to lymphocytes in the class II MHC context. Langerhans islets, dendritic, B and phagocytic cells form the APC group. The modulation of the function of the APC cells is very important in the self regulation of the immune system. The function on the immune response depends on the capacity of generating signals for the stimulation of T cells.