HIV Action on Lymphocytes

With regards to sexual transmission, HIV typically enters through disrupted mucosal surfaces, and then begins to replicate in T cells present in gut-associated lymphoid tissue, or GALT. The intestinal surface is lined with villi, which serves to absorb nutrients into the body, but just beneath that lining is a very high concentration of CD4+ T cells, many of which are already activated. The highest concentration of CD4+ T and other immune cells exist in the Peyer’s patches and mesenteric lymph nodes. These are the sites of immune induction, and the initiation of T-cell education and maturation. Within the Peyer’s patch are various immune cells including T and B cells, macrophages, and dendritic cells. During HIV infection, the virus travels to the gut and crosses the epithelium. It infects activated CD4+ T cells and replicates within. As part of the mode of replication, the virus destroys the host cell, releasing more of the virus into the surrounding area to infect new cells. The infection propagates across the area, resulting in a profound loss of CD4+ T cells. HIV spreads to secondary lymphoid organs through lymphatic and circulatory systems. HIV mainly replicates in CD4+ T cells in the GALT and secondary lymphoid organs, such as the spleen and lymph nodes. There is also viral replication in other CD4+ cells (namely macrophages and possibly dendritic cells), but how much that contributes to the pathophysiology of HIV disease is a matter of debate. During chronic HIV infection there is profound depletion of CD4+ T cells in the GALT and secondary lymphoid organs with destruction of the architecture of these organs and loss of immune and barrier function.