Opsonic recognition of staphylococci mediated by cell wall peptidoglycan: antibody-independent activation of human complement and opsonic activity of peptidoglycan antibodies.

In an effort to determine the cell surface component(s) of importance in the opsonic recognition of staphylococci, the interactions of intact bacterial cells, isolated cell walls, and purified cell wall components with human complement (C) and immunoglobulins were investigated. Intact cells of five strains of Staphylococcus aureus and one strain of Staphylococcus epidermidis were found to consume human C via both the classical and the alternative pathway. Activation of C resulted in the deposition of opsonically active C3 molecules on the surface of the staphylococci. All cell wall components contributed to the consumption of C via the antibody-dependent classical pathway. Activation of the alternative C pathway, however, was mediated exclusively by the pepti-doglycan moiety of the staphylococcal cell wall. The other major cell wall components, teichoic acid, lipotei-choic acid, and protein A, were without effect on the alternative pathway. Staphylococcal opsonization in human agammaglobulinemic serum (immunoglobulins ≃ 0.5% of normal) was also mediated by peptidoglycan and involved activation of the alternative C pathway. Kinetic studies revealed that C activation, C3 fixation, and opsonization proceeded at a slower rate via the alternative pathway than when both pathways were used. Optimal opsonization of staphylococci, therefore, requires immunoglobulins as well as an intact classical pathway. The capacity of peptidoglycan to absorb heat-stable opsonins from immune serum and the ability of the eluted peptidoglycan antibody to promote phagocytosis of staphylococci by human polymorphonuclear leukocytes provide further evidence for the key role of peptidoglycan in the opsonic recognition of staphylococci by the human host, and it is suggested that this may be true for other Gram-positive bacterial species as well.