Journal of Experimental Medicine, Vol 143, 1186-1198, Copyright © 1976 by Rockefeller University Press
Immunity to the group B streptococci: interaction of serum and macrophages with types Ia, Ib, and Ic
BF Anthony
The opsonization and phagocytosis of group B streptococci of types Ia, Ib,
and Ic were studied in vitro by measuring the uptake of radioactivity by
coverslip cultures of rabbit alevolar macrophages during incubation with
radiolabeled, nonviable bacteria which had been exposed to rabbit serum.
The uptake of counts per minute was quantitative, reproducible, and
reversibly inhibited by cold, indicating that it was largely a measurement
of phagocytic ingestion rather than of attachment of
bacteria-immunoglobulin complexes to macrophage membranes. Moreover,
suspended macrophages killed approximately 90% of viable streptococci in
the presence of specific antiserum. The opsonic activity of immune serum
was heat stable, and phagocytosis of streptococci was insignificant after
incubation with normal serum and antiserum to some heterologous group B
streptococci. By absorption studies, it was possible to identify the effect
of antibodies to specific bacterial antigens. Phagocytosis of streptococci
containing the corresponding antigens was maximal after opsonization with
homologous or heterologous sera containing antibody to IaCHO, IbCHO, or Ibc
protein. Phagocytosis of all three serotypes was intermediate when
opsonization could be attributed to anti-IabcCHO. The opsonization of a
specific group B streptococcus is complex and may involve two or more
antigen-antibody systems.
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