The A and the extended V N-terminal regions of streptococcal protein I/IIf mediate the production of tumour necrosis factor α in the monocyte cell line THP-1

The induction of tumour necrosis factor (TNF)-alpha from the monocytic cell line THP-1 by the streptococcal antigen I/II from Streptococcus mutans serotype f (protein I/IIf) was studied by use of recombinant polypeptides containing discrete domains of the protein. The derivatives carrying the N-terminal alanine-rich region (A region) and the adjacent variable region (extended V region) of the protein bound to THP-1 cell extracts in a saturable fashion, and one derivative lacking both the A and the extended V regions was not able to bind monocyte cell extracts, suggesting that the domains responsible for the binding of protein I/IIf to monocytes were the A and the extended V regions. Sodium metaperiodate pretreatment of THP-1 cell extracts, tunicamycin pretreatment of monocyte cells or competition with N-acetyl neuraminic acid (NANA) and fucose resulted in a 45-70% reduction in binding activity of the derivatives carrying the extended V region, demonstrating the lectin-like mode of recognition of the monocytic receptor by the extended V region and the role of NANA and fucose in this recognition process. Besides, the stimulation of monocytes to release TNF-alpha by the derivatives containing the A region and the extended V region was effective and was not affected by the addition of polymyxin B or vitamin D-3, suggesting that CD14 does not play the role of receptor in stimulation of monocytes by protein I/IIf to release TNF-alpha.