We have analyzed HLA class II alleles in a group of 153 Czech children with
rheumatoid arthritis by PCR and hybridization with
oligonucleotide probes. When we try to find a common sequence for all DRB1 alleles involved in juvenile and adult
arthritis, we can notice hydrophobic
amino acid at position 74, which is present in all these alleles, but not in nonsusceptible alleles, where is the hydrophilic
amino acid at position 74. In our model, we speculate that the hydrophilic
amino acid at position 74 creates a such kind of
epitope which is not suitable for rheumatoid-associated
peptides or T cells, and only hydrophobic
amino acid can permit binding of these
peptides or recognition by certain T cells. Analyses of the DPB1 sequences have shown that alleles which have a negatively charged
amino acid at position 69, are more frequent in pauciarticular patients while those with a positively charged
amino acid are more frequent in polyarticular patients. A positively charged
amino acid at position 69 might present the same rheumatoid associated
peptide as susceptible DRB1 alleles. The presence of more rheumatoid-associated
peptide on the cell surface may cause conversion to more severe polyarticular forms. A negatively charged
amino acid at position 69 could not present this
peptide and a low concentration of the
peptide on the cell surface presented just by DRB1 molecules keeps disease in a relatively benign condition of pauciarticular forms.