CD4 and scrub typhus: Although a few studies have shown that IgG responses in recovered scrub typhus patients only persist for a short period,12, 20, 21 the majority of these studies used whole bacteria as antigens for immunofluorescence assays (IFA), and antibody responses against specific protein antigens were measured by the total IgG or IgM level.22 Moreover, CD4 or CD8 T-cell responses specific to protein antigens of O. tsutsugamushi have been poorly characterized in scrub typhus patients, despite their functional importance in protective immunity.