Costimulatory molecule programmed death-1 in the cytotoxic response during chronic hepatitis C

Table 1 Summary of CD28 family co-stimulatory and co-inhibitory pathways

Receptor	Expression	Ligand	Ligand expression	T cell response regulation
CD28	T cells (naive and some memory)	CD80	B, T and DC, macrophages	Positive
PD-1	Activate T cells, B cells, macrophages	PD-L1 PD-L2	B, T and DC, macrophages, non-lymphoid cells (pancreas, placenta, heart)	Negative
CTLA-4	Activate T cells and regulatory T cells	CD80 CD86	B, T and DC, macrophages	Negative
BTLA	B and T cells	PD-L2	Macrophages, DC	Negative
		B7-H3	T and B cells, NK
		B7-H4
ICOS	T cells (memory and effector)	ICOS-L	B, T cells, macrophages and DC	Positive