Molecular or antigenic mimicry is a term for the similarity of different
antigens, which can be confused by the immune system.
Antigen recognition by
antibodies and
T cell receptors is specific, but not restricted to a single
antigen. Both types of receptors specifically recognize
antigens and are expressed with a very high but still restricted variability compared to the number of different
antigens they potentially could bind.
T cell receptors only can bind to
antigen peptides presented on certain self-MHC-molecules by screening only some
amino acid side chains on both the presented
peptides and the MHC molecule. The other
amino acids of the
peptide are not directly perceived by the T cell, offering the opportunity for a single T cell to recognize a variety of different
antigens with the same receptor, which significantly increases the immune repertoire. The immune system is usually tolerant to
autoantigens, especially to those of immune privileged sites, like the eye. Therefore,
autoimmune diseases targeting these organs were hard to explain, unless a T cell is activated by an environmental
peptide (e.g. pathogen) that is similar, but not necessarily identical with an
autoantigen. Here we describe antigenic mimicry of
retinal autoantigens with a variety of non-ocular
antigens resulting in the induction of intraocular
inflammation. T cells that are activated by mimotopes outside of the eye can pass the blood-retina barrier and enter ocular tissues. When reactivated in the eye by crossreaction with
autoantigens they induce
uveitis by recruiting inflammatory cells.