Specific absorption of human serum albumin, immunoglobulin A, and immunoglobulin G with selected strains of group A and G streptococci

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Abstract
Gram-positive bacterial strains (5) were selected for absorption studies of human serum samples. Strain AR1 (group A, M-type 1) and G148 (group G), with strong immunoglobulin(Ig)G binding capacities and strain AW43 (group A, M-type 60), binding IgA1 and IgA2, were compared with Staphylococcus aureus Cowan I and with S. epidermidis L603. AR1 and G148 could completely absorb out serum IgG. S. aureus Cowan I left a fraction unabsorbed, as expected from its known lack of IgG3 binding. Strain AW43 absorbed out all serum IgA, using a 10 .mu.l bacterial pellet for 20 .mu.l of serum. Serum IgM levels were slightly reduced by S. aureus Cowan I absorption. A bacterial mixture was designed consisting of S. aureus Cowan I and group A Streptococcus strains AR1 and AW43, with absorption characteristics suitable for use in discriminating between early IgM and late IgG and IgA immune responses in routine serological work. A new type of bacteria-mammalian protein binding was discovered. Human serum albumin was completely absorbed out by strain G148 and to a lesser extent by strain AR1 and AW43. S. aureus Cowan I and S. epidermidis were negative. The binding capacity of G148 for albumin equaled that of Cowan I for IgG. The binding pattern of albumin to the strains was different from those of IgG, IgA, IgM, fibrinogen, haptoglobin or aggregated .beta.2-microglobulin and may represent another type of bacterial-mammalian interaction with a specific albumin receptor on the surface of streptococci.