Human antibodies to phosphocholine. IgG anti-PC antibodies express restricted numbers of V and C regions.

We examined the IgG subclass composition and isoelectric focusing (IEF) spectrotype pattern of naturally occurring human IgG antibodies that bind phosphocholine (PC) and found direct evidence for restricted expression of both V and C regions among these antibodies. In most individuals, the isotype of these IgG anti-PC antibodies was primarily IgG2. However, serum from some individuals contained significant amounts of IgG1 and IgG3 anti-PC antibodies. We also found that in individual sera, anti-PC antibodies are pauciclonal, as demonstrated by restricted spectrotypic patterns of the anti-PC antibodies. The IEF pattern of these antibodies were for the most part unique for each individual. In some sera, certain anti-PC antibodies with isoelectric points of basic pH bound PC conjugated to bovine serum albumin (PC-BSA) but did not bind pneumococcal C-carbohydrate bearing PC determinants. In two individuals, we found that the spectrotypes that bound only PC-BSA were of the IgG1 subclass. Taken together, these findings demonstrate that within individual sera, human antibodies to PC are quite restricted in both V and C region expression, and furthermore, these V and C regions of human Ig may not randomly associate.