A B S T R A C T In an effort to determine the staphylococcal cell surface component(s) of importance in opsoniization, cell walls (peptidoglycan and teichoic acid) and peptidoglycan were isolated from Staphylococcus aureus strain H grown in [3H]glycine-containing broth. After incubation of the cell walls and peptidoglycan with various opsonic sources, uptake by human pol'ymorphonuclear leukocytes wvas measured. The opsonic requirements for phagocvtosis of cell walls and peptidoglycan were found to be similar to those of intact bacteria. Removal of teichoic acid from the cell wall did not affect opsonization. Likewise, a teichoic acid-deficient mutant strain of S. aureus H was opsonized in a manner similar to that of the parent strain. Immunoglobulin G functionied as the major heat-stable opsonic factor and both the classical and alternative pathways participated in opsonization. Kinetic studies revealed that opsonization of peptidoglycan, as well as C3-C9 consumption by peptidoglycan, proceeded at a slower rate via the alternative pathway (C2-deficient serum) than when the classical pathway was present (normal serum). The ability of peptidoglycan to activate C3-C9 was significantly reduced when normal and C2-deficient sera were preabsorbed with peptidoglycan at 2°C suggesting that antibodies to peptidoglycan may be involved in activation of'both the classical aind alternative complemenit pathways. Thus, peptidoglvcan appears to be the kev cell wall comiipoineint iinvolved in staphylococcal opsonlizationi, aind it is suggested that host response to peptidlogl-can, a major cell wall component of most gramn-positive bacteria, max be related to the develop-

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