His studies on immunophenotyping and innate immunity in HIV disease have made significant contributions to this field. These early studies were carried out in a newly recognized population of hemophiliacs that were shown to develop AIDS. This work was extended with more recent publications using multi-parameter flow cytometry to define monocyte subsets and the critical role of monocytes and innate immune cell activation in HIV pathogenesis. These papers have contributed to a shift in thinking about HIV as an adaptive immune disease to one focused on innate cell driven inflammation linked to the development of immunosenescence.