title: Natural immunity to bacterial infections: the relation of complement to heat-labile opsonins.
abstract: Heat-labile opsonins to pneumococci in normal mammalian sera, unlike antibodies, fail to interact with the bacteria at 0 degrees C and require Ca(++) and/or Mg(++). They are readily removed from serum by antigen-antibody complexes that fix complement (C) and are inhibited by reagents that inactivate various C components. The principal heat-labile opsonin to pneumococci is activated C3 (C3(b)), but a slight enhancing effect is exerted by one or more of the late-reacting components of the hemolytic complement system (C5-C9). Since heat-labile opsonins are immunologically polyspecific, they presumably play a broad protective role in the early (preantibody) phase of acute bacterial infections.
mesh_terms: D000818:Animals; D003165:Complement System Proteins / Q000494:pharmacology*; D006168:Guinea Pigs; D006358:Hot Temperature; D009895:Opsonin Proteins; D010587:Phagocytosis; D011008:Pneumococcal Infections / Q000276:immunology*; D051381:Rats; D013296:Streptococcus pneumoniae / Q000276:immunology
chemical_list: D009895:Opsonin Proteins; D003165:Complement System Proteins