It has previously been identified that fractalkine potently induces chemotaxis of CX3CR1+ monocytes, natural killer cells and CD4+ T cells [23] and, in mouse models of asthma, we have learned that RV infection propagates infiltration of lymphocytes and natural killer cells into the lungs, however the precise chemotaxis axis involved has not yet been determined [31, 32]. This evidence concerns the gene CD4 and asthma.