CD40LG and infection: However, the use of plasma or serum as positive control has several significant drawbacks, including low stability, high cost [11,12], difficulty in economically viable large-scale production because the decline in the concentration of IgM antibodies against HEV is steeper than that of total Ig during the first 3 months [13-15], and potential infection with reported 51% PCR positive when both IgG and IgM was present in serum [16].