Reduced opsonisation of protein A containing Staphylococcus aureus in sera with cryoglobulins from patients with active systemic lupus erythematosus.

Among a total of 41 patients with systemic lupus erythematosus (SLE) 11 of 14 patients with active disease had reduced capacity (p less than 0.05) to opsonify Staphylococcus aureus in undiluted sera, as compared with nine of 27 patients with inactive disease (p less than 0.02). The opsonic reduction in the active patients increased with the number of active organ systems (p less than 0.002). No correlation was found between reduced opsonisation and corticosteroid treatment, or serum concentrations of complement components (C) of the classical pathway, or bacteria-associated activated C3. When the cryoglobulin fraction of immune complexes (IC) was removed, normal opsonic capacity was restored, and the opsonic reduction could be transferred with the cryoglobulins to pooled serum. Increased IC values, as measured by C1q binding assay, were found in conjunction with reduced opsonic capacity (p less than 0.04). Since opsonisation in SLE sera of a protein A deficient strain of S. aureus was normal, reduced S. aureus phagocytosis in SLE sera may be explained by IC binding to staphylococcal protein A.