Comparative analysis of immunological properties of S-layer proteins isolated from Lactobacillus strains

Previous studies have suggested that some Lactobacillus S-layer proteins could modulate immune responses. Primary structures of the S-layer proteins are variable, and their immunological differences are poorly understood. In this study, we evaluated the immunological properties of eight distinct S-layer proteins from different Lactobacillus species. We found that removal of the S-layer proteins from the cell surface reduced the immunological activities of Lactobacillus cells in THP-1 cells. Furthermore, the purified S-layer proteins induced the production of IL-12 p40, although their immunological activities varied between the different S-layer proteins. The production of IL-12 p40 was notably induced by the S-layer protein SLP(aly) from Lactobacillus amylolyticus NRIC 0558^T. Multiple sequence alignment revealed that the percent identity of the S-layer proteins of the eight strains vary from 10 to 90 %. In particular, N-terminal regions showed high levels of diversity. To obtain more information about their structure and the immunogenicity, truncated and chimeric S-layer proteins were constructed in recombinant E. coli. Profiling of cytokine production in THP-1 cells by truncated and chimeric S-layer proteins suggested that the intact conformation of the N-terminal region of SLP(aly) contributes to high immunogenicity.