Induction of myosin cross-reactive antibody and cytolytic T cell responses in mice with Streptococcus pyogenes

Abstract

Induction of Myosin Cross-Reactive Antibody and Cytolytic T Cell Responses in mice with Streptococcus pyogenes Cynthia Cunningham Impetigo and pharyngitis are two common suppurative infections in man elicited by Streptococcus pyogenes that lead to autoimmune complications in susceptible individuals. Although the underlying mechanisms for the onset of post-streptococcal autoimmunity have yet to be established, experimental information gained thus far suggests that the resultant pathology is a consequence of immunological cross-reactivity between streptococcal antigens, namely the anti-phagocytic factor M protein and host proteins, specifically myosin. Experimental animal model systems developed to date have predominantly relied on the immunization of adult animals with M protein emulsed in adjuvant. In the laboratory we have undertaken studies with mice to examine the capacity of S. pyogenes as whole organism without adjuvant to elicit autoreactive B and T lymphocytes. We have observed that immunizing mice with heat-killed preparations of S. pyogenes as neonates, but not adults, induces the production of host cross-reactive serum antibodies akin to those documented in cases of post-streptococcal autoimmunity. Western blot analysis of monoclonal antibodies generated from mice immunized with S. pyogenes suggests that antibodies induced in neonatal mice preferentially recognize the cardiac isoforms of mouse skeletal myosin, whereas, antibodies derived from adult mice primarily recognize determinants shared by all isoforms of mouse skeletal myosin. In addition, we have demonstrated the ability of neonatal, but not adult, mice to mount a myosin-reactive CD8 + cytotoxic T cell response following immunization with S. pyogenes. Our observations indicate that the response is additionally dependent on the genetic background of mice, the route of immunization, and requires M protein. In summation, our results suggest that in susceptible individuals exposure to S. pyogenes early in life may serve as a priming event and following a subsequent event later in life, possibly re-exposure to S. pyogenes, allow the initiation of the pathology associated with poststreptococcal autoimmunity. These results contribute to the understanding of the development of the mechanisms of post-streptococcal autoimmune complications and may ultimately contribute to the development of effective diagnostic intervention strategies. iii Dedication I dedicate this dissertation to my parents, James and Judith McDaniel, whose example and uncompromising devotion and support have given me the courage to accept challenges and the strength to accomplish my goals.