Mycoplasma genitalium (MG) is a sexually-transmitted, reproductive tract pathogen of men (urethritis) and women (cervicitis, pelvic inflammatory disease, ectopic pregnancy, infertility) with a similar, or higher, prevalence as compared to Chlamydia trachomatis and Neisseria gonorrhoeae. Antibiotic resistance is increasing in MG isolates, with some infections totally untreatable with recommended regimens in the US. MG was included on the Watch List of the CDC 2019 Antimicrobial Threat Report, and was recognized as an understudied cause of PID at the November 2019 workshop ?New frontiers in STD-related pelvic inflammatory disease (PID), infertility, and other sequelae?. The recent FDA approval of two MG diagnostic tests (Hologic and Roche) will certainly increase public awareness of MG, and demands for improved treatments. Our laboratory has focused on understanding the ability of MG to persist for weeks to years despite the presence of specific antibodies in the genital tract, the variability of the immunodominant MgpB and MgpC adherence proteins, and the local and systemic antibody response to these proteins during infection. We demonstrated that MgpB and MgpC undergo phase and antigenic variation via a unique system of recombination between the mgpBC expression site and partial copies archived in the chromosome. In the parent grant (R21AI148816- 01), we extend these studies to define the epitopes and the consequences of antibody binding to the conserved and variable regions of MgpC. Further, we define the role of the newly identified MG281 antibody binding protein in evasion of the innate and specific immune response including binding to non-specific IgG and IgA, effect on MG complement resistance, and the effect of MG281 antibody binding on opsonophagocytic killing of MG. With this supplement application, we propose to expand Aims 2 and 3 of the parent award to identify domains within MG281 important for the function(s) of this unique antibody binding protein. As the structures of multiple MG281-Fab cocrystals are known, a series of precise, rationally-designed deletion and amino acid substitution mutations will be constructed and their effect on MG281 function measured in terms of antibody binding, resistance to antibody-mediated complement killing, and phagocytosis of MG. We hypothesize that MG281 protects MG from attack by innate immune defenses of the genital tract early in infection. As MgpB and MgpC are the dominant antigens targeted by patient antibodies, we further hypothesize that MG281 protects MG against killing by specific antibodies by preventing complement attack and opsonophagocytosis by genital tract immune cells. These experiments, along with our novel approaches pioneering experimental methods for the difficult field of mycoplasma research, will inspire improved prevention strategies to combat this increasingly antibiotic-resistant and important pathogen and provide a unique opportunity for undergraduate research experience. This proposal complements our accompanying application in which we seek funding for a second undergraduate student (Zoie Bailey) as suggested by PA-18-906 who will identify MG and serum proteins that interact with MG281, further expanding our understanding of MG281 function.
The proposed studies seek to understand how Mycoplasma genitalium (MG), a sexually-transmitted bacterium, causes reproductive tract disease in men and women. MG avoids killing by the host immune response enabling persistence for weeks to years if untreated, and is increasingly resistant to antibiotics. Our studies will explore the interactions between MG surface molecules and host immune effectors including specific and non- specific antibodies, complement, and phagocytes.
