The immune response to the parasitic nematode Trichinella and the ways to escape it. From experimental studies to implications for human infection.

The review describes different aspects of the host immune response to Trichinella, not only at the intestinal level on which most of the studies have focused until now, but also in the muscles which represent the final target of host invasion. The role of antibodies, T cells, mast cells, eosinophils and neutrophils, respectively, in immune reaction to this nematode is considered, in the light of the recent data derived from experimental models, both "in vivo" and more recently "in vitro" and when available, from clinical observations. A section is also devoted to the principal escape mechanisms from host immune responses, described in Trichinella, which are in part common to other parasites, in part peculiar. Two groups of mechanisms are described: antigen-dependent, such as anatomic seclusion, antigen stage-specificity, shedding and renewal and molecular mimicry, and those directly affecting the host immune response. Of the latter, some act at central level like immune suppression, polyclonal activation and eosinophilia induction, others interfere with effector functions as in the case of host leukocyte modification, immune complex accumulation, blocking antibody production or complement assembly blocking. The antigenic composition of the different stages is the subject of another section which has the aim to give an overview of the principal antigens described up to now, without giving too many biochemical details, but just illustrating the candidates for possible vaccines. Finally, the perspectives for vaccination are described. Most of the results described are derived from the experimental studies, but their implications in human infection are relevant.