The inference of antigen selection on Ig genes

Analysis of somatic mutations in V regions of Ig genes is important for und erstanding various biological processes. It is customary to estimate Ag sel ection on Ig genes by assessment of replacement (R) as opposed to silent (S ) mutations in the complementary determining regions and S as opposed to Ii mutations in the framework regions. In the past such an evaluation was per formed using a binomial distribution model equation, which is inappropriate for Ig genes in which mutations have four different distribution possibili ties (R and S mutations in the complementary-determining region and/or fram ework regions of the gene). In the present work, we propose a multinomial d istribution model for assessment of Ag selection, Side-by-side application of multinomial and binomial models on 86 previously established Ig sequence s disclosed 8 discrepancies, leading to opposite statistical conclusions ab out Ag selection. We suggest the use of the multinomial model for ail futur e analysis of Ag selection.