Functional and Developmental Analysis of CD4+CD25+ Regulatory T Cells under the Influence of Streptococcal M Protein in Rheumatic Heart Disease

The purpose of this study was to determine the role of streptococcal M protein in naturally-occurring CD4+CD25+ regulatory T cells (nTregs) function and development in rheumatic heart disease in Iraqi patients. Streptococcus pyogenes was isolated for subsequent M protein extraction. Also, peripheral blood nTregs and CD4+ T cells were isolated by using Magnetic Cell Separation System. Tissue culture for isolated cells was performed in the presence and absence of M protein. Cell count was performed, and tumor necrosis factor alpha (TNF-α) and interleukin-4 (IL-4) were determined in culture supernatant using ELISA system. There was a significant positive correlation (P<0.01) between the number of proliferated nTregs and CD4+ T cells in the presence as well as the absence of streptococcal M protein. Moreover, there was a significant negative correlation between the mean number of nTregs and CD4+ T cells in mixed culture system in the absence of M protein (r=-0.995). There was also a positive, but not significant (P>0.05), association (r=0.353) between the mean number of nTregs and CD4+ T cells in the presence of M protein. The M protein stimulated CD4+ T cells to produce IL-4 in very little amount (<4 pg/ml) in all samples. Compared to the production of IL4, TNF-α was produced in higher concentrations in the culture supernatants. The findings of the study indicate that streptococcal M protein has an important role in increasing the proliferation of CD4+CD25+regulatory T cells and CD4+ T cells. However, CD4+CD25+ regulatory T cells have lower suppressive activity against CD4+ T cells in the presence of M protein.