Relationship between HLA class I genotype and CD4⁺ T-cell levels. (A) Percentage of CD4⁺ T cells as determined by flow cytometry in peripheral blood (PB, closed symbols) and rectal mucosa (RMC, open symbols) among controllers and noncontrollers with and without protective class I HLA alleles. (B) Percentages of CD4⁺ T cells in peripheral blood (PB, closed symbols) and rectal mucosa (RMC, open symbols) among persons with or without protective class I HLA alleles, defined as in Figure 5, irrespective of clinical status. Horizontal bars represent the median for each group. *P < .05, **P < .01, ***P < .001.