Regulatory T cells are CD4+,CD8+ and FoxP3+. The basic function of these cells is to down regulate the immune system. These cells are important for the "self check mechanism" to prevent auto immune diseases. 

State University of New York at Buffalo

T lymphocytes, which are commonly called T cells, express T cell receptors (TCRs) on their surface.  These are transmembrane proteins that bind to processed antigens that are presented by antigen presenting cells (ATCs).  
There are three types of T cells, differentiated on the basis of their functions:
1. Cytotoxic T- cells
2. Helper T cells 
3. Regulatory T cells

T Lymphocytes

Cytotoxic T cells are known to be CD8+. CD markers are surface proteins used to identify immune cells. The function of cytotoxic T cells is to directly kill the antigen infected cell by releasing certain cytotoxic substances in the cell which include granzyme and lysozyme. Cytotoxic T cells recognise MHC class 1 molecules that act as antigen presenting cells for the CD8+ cells. 

Function of Cytotoxic T cells

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.

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