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The HLA-E protein is one of the most extensively studied MHC class Ib antigens and the least polymorphic one compared to other MHC class I molecules. In the human population there have been reported just ten alleles encoding three different peptides. Only two of these alleles, namely HLA-E*0101 and HLA-E*0103, are widely distributed (around 50% each). The proteins encoded by these alleles differ from each other in one amino acid at position 107. In HLA-E*0101 it is arginine and in HLA-E*0103 it is glycine. The difference between these proteins manifests itself in surface expression levels, affinities to leader peptides and thermal stabilities of their complexes. The HLA-E molecule is a ligand for CD94/NKG2 receptors on NK cells and TCR receptors on NK-CTL (NK-cytotoxic T lymphocyte) cells, so it plays a double role in both innate and adaptive immunity. This paper reviews the knowledge on the role of the HLA-E molecule in the immunological response. Aspects related to polymorphism of the HLA-E gene and the course of several diseases including type I diabetes, ankylosing spondylitis, HCV and HIV infections, nasopharyngeal cancer and recurrent spontaneous abortions, as well as the outcome of hematopoietic stem cell transplantation, are presented and discussed in more detail.

Structural and functional homology between bacterial proteins and host antigens, called molecular mimicry, is considered as significant pathogenic factor involved in several autoimmune diseases. The most important examples of this phenomenon reviewed in this work, involve rheumatic fever, Graves' disease, ankylosing spondylitis, Reiter's syndrome and rheumatic arthritis caused by infections with Streptococcus, Yersinia, Klebsiella, Escherichia coli, respectively.

Immunological studies are widely applicable at a clinic in rheumatoid patients, despite the fact that their clinical value is still a disputable subject. Many authors are of opinion that the determination of individual immunological tests does not provide the estimation of immunological state in patients, and should be evaluated critically. The aim of the actual paper was to evaluate the immunological state of patients with rheumatoid arthritis by means of immunological profile index, which consists in performing concurrently many immunological tests involving both humoral immunology and cellular one. The results were referred to the duration of the disease, pathological process activity, the presence of rheumatoid factor, the advancement of osseous changes. The studies were carried out in patients, aged 16-69 years, 63 of them had RA and 9 were affected by ankylosing spondylitis. The control group comprised 16 normal subjects aged 28-61 years. It has been disclosed that the values of the immunological profile index in patients were statistically significantly lower than in the control group. The lowest values of immunological profile index were recorded in patients with extra-articular symptoms with recurrent infections of urinary and respiratory tracts, as well as in patients with active form of RA, and the presence of rheumatois factor. The patients with ankylosing spondylitis were found to reveal immunological disorders, but they were expressed less markedly than in RA patients. With the help of immunological profile it was possible to show that multifunctional immunological disorders appeared in patients with rheumatoid arthritis. The most sensitive immunological tests were: levels of immunoglobulins in blood serum, and the count of lymphocytes T and B. The immunological profile study in patients with rheumatoid inflammation of joints is an objective method of evaluating their immunological state.