CD4 and AIDS: Inhibitory KIR3DL1 and its activating KIR3DS1 counterpart are associated with slower time to the acquired immunodeficiency syndrome (AIDS) (using the 1987 definition for AIDS of the US Centers for Disease Control and Prevention), time to CD4 counts of >200 cells/mm3, HIV viral load control and in the case of KIR3DS1 protection against opportunistic infection late in disease, when co-expressed with certain Bw4 allotypes (12, 13, 77).