CD40LG and dengue disease: However, when IgM immunoreactivity indexes for both Dengue and Chikungunya were assessed either in the presence or absence of SARS-CoV-2 IgG antibodies, a significant reduction in IgM immunoreactivity index was observed for Chikungunya/SARS-CoV-2 samples (Fig 7A) but not for Dengue (Fig 7B).