With the discovery of this wide array of possible CD4+ T-cell subsets and their different activation requirements and functional capacities, it is becoming clear that CD4+ T-cells may not be simply defined as individual subsets of Th cells producing a single cytokine, but rather they represent components of a dynamic and interactive response, in which these cells can be multifunctional, flexible, and plastic depending on the disease/infection and activation environment (61). Here, CD4 is linked to infection.