Effects of experimental protein-containing pneumococcal preparations on maturation of murine dendritic cells

Abstract

Dendritic cells as the most active and highly specialized antigen presenting cells, play a key role in initiating immune responses. Currently, generation of medications activating dendritic cells for development of anti-infective and anticancer vaccines is of highly relevance. Preparations of microbial origin are promising to augment activity of dendritic cells, because they carry innate immune ligands for Toll-like receptors. Such preparations include experimental protein-containing pneumococcal preparations, obtained from acetone-inactivated microbial mass of the deposited S. pneumoniae 6B vaccine strain No. 296, followed by aqueous extraction and separation of 30—100 kDa fraction. Dendritic cells were obtained from bone marrow cells of CBA mice (n = 15), and cultured in complete growth medium RPMI-1640 added with recombinant GM-CSF and IL-4 (Biosource, USA). On day 6, experimental protein-containing pneumococcal preparations (50 pl/ml) were administered to the cultured immature dendritic cells. Commercial TNFa (20 ng/ml, Biosource, USA) was used as a standard maturation inducer (positive control). Immunophenotyping of dendritic cells was conducted by using flow cytometry with FITC- and PE-labeled monoclonal antibodies against cell surface receptors: CD34, CD38, CD83, CD86, CD80, CD11c, MHC II, CD14, CD282 (TLR2), CD284 (TLR4), (eBioscience, USA). Studying an effect of preparations on maturation of dendritic cells revealed that morphological characteristics of dendritic cells generated by using experimental protein-containing preparations did not differ significantly between each other as well as those induced by TNFα. The cells were characterized by large sizes, oval or irregular shape, veiled cytoplasm, eccentrically located nucleus and numerous long thin protrusions. Experimental proteincontaining preparations induced in cultured dendritic cells decrease in count of CD34+ immature and TLR2/TLR4+ cells, increased count of cells expressing markers of adhesion (CD38+), activation (MHC II+), costimulation (CD80/ CD86+) and terminal differentiation (CD83+), which may evidence about events of differentiation upon dendritic cell maturation. The 30—100 kDa fraction increased count of cells expressing adhesion molecules to a greater extent than aqueous extract that more pronouncedly stimulated rise in count of dendritic cells bearing costimulatory molecules (p < 0.05). The activity of the examined proteins regarding their effect on CD83+ cells was comparable. Experimental protein-containing antigens derived from pneumococcal vaccine strain were shown to induce maturation of dendritic cells from bone marrow precursors, induce a decrease in the count of TLR2 and TLR4-expressing cells accounting for activating effect on innate immune effectors.

Keywords

• experimental protein-containing pneumococcal preparations
• dendritic cells
• pneumococcus
• maturation induction
• immunophenotype
• morphological characteristics