Associations between different loci.

The Cramer’s V coefficient was used to measure association statistics with clonal complexes. The values indicated a strong association between antigen alleles and clonal complexes. The Standardized Index of Association IAS was used to test the stability of associations between different loci. The antigen pairs showed relatively high IAS values, indicative of strong, stable associations between the different loci over time. Moreover, the combinations showed a non-overlapping structure (measured by f* metrics) that suggested the immune selection maintaining antigenic combinations. §The three statistical parameters V, IAS and f* are based on the frequency of the alleles and vary between 0 (random distribution) and 1 (perfect association or non overlapping distribution in the case of f*).