CD4 and infection: Mechanistically, break down of the tight epithelial barrier of the gastrointestinal tract (GIT) results from a combination of factors, namely preferential infection and depletion of CCR5-expressing CD4+ T lymphocytes, accumulation of inflammatory cells and a concomitant decrease in cells that regulate epithelial homeostasis, alterations in the regulation of tight junction protein expression, and possibly epithelial and enterocyte apoptosis (3–5).