Previously, HLA-DR incorporation into the envelope of budding virions was demonstrated to enhance virion infectivity [45, 46] . To determine if CIITA-enhancement of virion infectivity was due to HLA-DR or other components of the class II antigen presentation pathway, we measured virion infectivity from cells expressing these proteins. However, virions from these cells were just as infectious as virions released from vector only controls, yet not as infectious as virions from cells either stably or transientlyexpressing CIITA ( Figure 2D ). Therefore, CIITA enhancement of virion infectivity is independent of the MHC class II antigen presentation pathway. Together, these data suggest CIITA has two effects on the HIV replicative cycle in producer cells, both of which are independent of the MHC II antigen processing pathway; i) it does not induce HLA-DR, mediated intracellular retention of Gag and ii) it increases the infectivity of HIV virions.