Functional subsets of B cells defined by quantitative differences in surface I-A.

The quantitative expression of surface I-A determinants has been used to define functional B cell heterogeneity based on responsiveness to the trinitrophenyl (TNP) hapten on various classes of carrier molecules. Unprimed, anti-Thy 1 and complement-treated B10.A (I-Ak) B cells were stained with a monoclonal anti-I-Ak reagent that had been fluorescein (FL) conjugated. By using a fluorescence-activated cell sorter these cells were then sorted into 2 populations of cells staining heavily or lightly with this reagent. These populations of cells were then assayed for anti-TNP precursor frequency, in responses to 3 TNP-antigens, by limiting dilution analysis. B cells responsive to TNP-lipopolysaccharide (LPS) and TNP-sheep red blood cells (SRBC) were found in both the B cells that expressed a low amount of surface I-A and the B cells that expressed a high amount of I-A. However, B cells with the ability to respond to TNP-Ficoll were found only in the B cells that expressed a low amount of surface I-A. These experiments suggest that the quantitative expression of surface I-A can be used to define B cell populations with different abilities to respond to hapten coupled to Ficoll.