Plaque formation by B cell colonies.

A method is described for routinely detecting secretion of antibodies by intact B cell colonies grown in soft agar. Protein A-coupled sheep red blood cells and hapten-conjugated sheep red blood cells were found to be suitable targets. Using this assay we have determined that approximately 1 in 3 B cell colonies contain cells secreting IgM while approximately 1 in 6 contain cells secreting IgG. We have also determined the frequency of clones which secrete antibodies which lyse TNP3-SRBC, NIP4-SRBC, NP4-SRBC, FITC5-SRBC, SRBC, and HRBC. This assay can be used to study the mitogen-induced maturation of clonable B cells into plaque-forming cells, to follow antigen-specific clonable B cells during an immune response, and unambiguously to detect B cell colonies when other colony types are present. The method is also suitable for morphological analysis of stained colony cells.