Helper T cells are known to be CD4+. Their basic function is to produce cytokines that up regulate the immune system and alert the other phagocytic cells. Helper T cells can be further divided into TH1, TH2 and TH17 cells. TH1 cells stimulate the CD8+cells and macrophages to kill the infected cells.TH2 cells stimulate B cells to produce antibodies. TH17 cells help maintain the mucosal barrier and is involved in auto-immunity. They are also involved in pro-inflammatory response as they recruit neutrophils and macrophages to site of infection. T helper cells recognise MHC class II molecules.