(A) Representative surface expression level histograms of CD3, CD4, major histocompatibility complex class I (MHC-I), CXCR4, and BST-2 in CD4loNef+ subpopulations after wild-type (WT) or Nef-G63E mutant simian immunodeficiency virus (SIV) infection at multiplicity of infection (MOI) 0.1 on HSC-F cells. The gene discussed is CXCR4; the disease is infection.