CD4 and infection: More recent in vitro studies though highlight CD25+ CD4+ Treg cells to restrain the vigour of diverse antigen-specific responses in humans, including those directed against tumours, parasitic, fungal, bacterial and viral antigens and consequently to be associated with the inability to clear infection of some pathogens [1]–[3], [5]–[6] or mount an effective immune response following immunization in in vivo murine model systems [7].