19 Heat Shock Proteins as Antigens in Immunity against Infection and Self

Abstract

I. INTRODUCTION
A major driving force for the evolution of the immune system is the continuous encounter with an almost infinite variety of invading pathogens. The immune system deals with this extreme diversity by generating an equally high number of receptors capable of specifically discriminating between these structures (Nossal 1993). The following are the two types of receptors: (1) antibodies that are produced by B lymphocytes and recognize their counterparts directly and (2) T-cell receptors that are expressed on the surface of T lymphocytes and recognize their counterparts indirectly. The diversity of both types of receptors is generated by similar mechanisms, in particular genetic recombination. The molecular entities recognized by these receptors are termed antigens. Antibodies recognize “their” antigens directly, comprising a stretch of six to seven amino acids or five to six carbohydrate residues on proteins or carbohydrates, respectively. Antibodies are therefore particularly suited to contest microbes and microbial secretory products present in the extracellular space. T cells recognize their antigens indirectly, i.e., they interact with oligopeptides of about nine amino acids in length that are presented by self-structures. Hence, antigen recognition by T cells requires intracellular processing of microbial components and subsequent presentation on the cell surface by specialized molecules that are the products of the major histocompatibility gene complex (MHC) (Janeway 1993). T cells are therefore particularly equipped for opposing microbes living inside host cells. In a given setting, the immune system will contact certain invaders more frequently than others. To focus the immune response to these...