Humans with acute Q fever develop serum IgM, IgG, and IgA titers against C. burnetii antigens that persist for long periods after resolution of infection, while those with chronic Q fever have very high phase I IgG and significantly lower phase II IgM titers (Worswick and Marmion, 1985; Buijs et al., 2021). Here, CD40LG is linked to infection.