Rapid and extensive deposition of fibrous tissue called collagen in the lymphatic tissue of the gut during HIV infection has been linked to the dramatic and enduring depletion of CD4 cells from the gut. The findings, published in the August 15th issue of Journal of Infectious Diseases, may provide insight into one of the long-standing mysteries of HIV treatment, namely why antiretroviral therapy, which is successful in reconstituting blood CD4 levels, is considerably less potent in the gut.
http://www.aidsmap.org/en/news/4E76EB88-AD1D-4AFE-B9A8-B6236229DDAC.asp