It has been subsequently shown that the immune regulatory role of IL-10-producing Tr1 may differ between primary and secondary infection in blood stage Plasmodium infection: IL-10 may exert a more suppressive effect on the innate immune system, specifically MHC-II expression on APCs, during primary infection while it suppresses the adaptive system, specifically expansion of antigen-experienced memory CD4 T cells, in secondary infections [320]. Here, CD4 is linked to infection.