Sarcoidosis, cancer and molecular mimicry.

Molecular mimicry seems to be the most important factor for the heterogeneous clinical presentation and the immunopathogenesis of sarcoidosis. Molecular mimicry may occur as a result of altered activity of oncogenes. This can lead to crossed-type mediated body reactions targeting structurally similar sections or regions from the tissue homeostasis. Available data suggest that structural analogy between tissue and foreign or de novo-appearing peptides is not always reliable. Nevertheless, lack of amino acid identity between the tissue and the de novo-generated tumour antigens does not exclude the phenomenon of molecular mimicry as the major generator of sarcoidosis. There is growing evidence of the mimicry phenomena, caused not only by the similarity between the amino acids but also between the elements which connect segments in the immunological cascade and which may also be affected by external factors. Molecular mimicry may occur between two identified peptides having similar antigenic surfaces (transitory or not), in the absence of a primary homology in amino acid sequence. As far as tumour antigens are concerned, a structural analogy to the de novo-appearing tumour antigens is more likely than transitory imitation resulting from the additional interference of other physical forces. Further research should be performed to confirm, or reject, the transitory imitation thesis or hypothesis.