Mycobacterium tuberculosis modifies cell wall carbohydrates during biofilm growth with a concomitant reduction in complement activation.

The development of new vaccines for TB needs to be underpinned by an understanding of both the molecular and cellular mechanisms of host-pathogen interactions and how the immune response can be modulated to achieve protection from disease. Complement orchestrates many aspects of the innate and adaptive immune responses. However, little is known about the contribution of the complement pathways during TB disease, particularly with respect to mycobacterial phenotype. Extracellular communities (biofilms) of M. tuberculosis are found in the acellular rim of granulomas, during disease, and these are likely to be present in post-primary TB episodes, in necrotic lesions. Our study aimed to determine which mycobacterial cell wall components were altered during biofilm growth and how these cell wall alterations modified the complement response. We have shown that M. tuberculosis biofilms modified their cell wall carbohydrates and elicited reduced classical and lectin pathway activation. Consistent with this finding was the reduction of C3b/iC3b deposition on biofilm cell wall carbohydrate extracts. Here, we have highlighted the role of cell wall carbohydrate alterations during biofilm growth of M. tuberculosis and subsequent modulation of complement activation.