QUANTITATION OF THE UPTAKE OF HUMAN IgG BY SOME STREPTOCOCCI GROUPS A, B, C AND G

The uptake of IgG by streptococci irrespective of the antibody combining sites was studied with a method using 125I labelled pooled human IgG and human IgG myeloma proteins. When 1 μg IgG was added it proved possible to quantitate the uptake of IgG within a standard deviation of 3 per cent. The results expressed relative to the 1.0 μg IgG added were: group A, type M 56: 20.4±1.4 per cent, group B, strain 123 B: 40.8±1.6 per cent, group C, strain 81 C: 44.9±1.9 per cent and group G, strain 113 G: 47.0±2.8 per cent. When IgG was added in excess, two of the streptococcal strains, group A, type M 1 and group G, strain 113 G were able to take up about one third of that bound by a similar number of the S. aureus, Cowan I. Only minor differences were seen between the uptake by the streptococci of a given amount of four randomly selected purified myeloma proteins of IgG subclasses 1, 2, 3 and 4 and pooled human IgG with the exception of a group G strain which took up a smaller amount of IgG 3 myeloma protein. Trypsin treatment and heating of the streptococci at 100° C for 15 min reduced the uptake of IgG by streptococci to a certain extent while heating of the streptococci at 56° C for 30 min did not alter the uptake of IgG. Lancefield extract of group A, type M 56 streptococcus inhibited such uptake of IgG.