T cells in immune system - (Mar/06/2006 )

hello, i came across this question and is confusing cause i think all of them except the IgT cell improves the immune response, anyway maybe some one here knows more and can give me an opinion;

which type of T cell improves the immune response?

1- helper t cell
2- supressor t cell
3- cytotoxic t cell
4- memory t cell
5- IgT cell

hi
first find in google what is an IgT cell and come back with the response...