n 1  :  an antigenic protein of Group A streptococci that is found on the cell wall extending into the surrounding capsule, is variable among the different serotypes, and confers streptococcal virulence by protecting the cell from phagocytotic action - called also M substance   2  :  a monoclonal antibody that is produced by plasma cells abnormally proliferating from a single clone and that is characteristic of monoclonal gammopathy .
 
 
 
Similar sounding terms:  me·per·i·dine 
 
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