HIGHLIGHTSd Cross-sectional study of 44 hospitalized COVID-19 patients d RBD-specific IgG responses detectable in all patients 6 days after PCR confirmation d Neutralizing titers are detectable in all patients 6 days after PCR confirmation d RBD-specific IgG titers correlate with the neutralizing potency

28SARS-CoV-2 is currently causing a devastating pandemic and there is a pressing need to 29 understand the dynamics, specificity, and neutralizing potency of the humoral immune response 30 during acute infection. Herein, we report the dynamics of antibody responses to the receptor-31 binding domain (RBD) of the spike protein and virus neutralization activity in 44 COVID-19 32 patients. RBD-specific IgG responses were detectable in all patients 6 days after PCR 33 confirmation. Using a clinical isolate of SARS-CoV-2, neutralizing antibody titers were also 34 detectable in all patients 6 days after PCR confirmation. The magnitude of RBD-specific IgG 35 binding titers correlated strongly with viral neutralization. In a clinical setting, the initial analysis of 36 the dynamics of RBD-specific IgG titers was corroborated in a larger cohort of PCR-confirmed 37 patients (n=231). These findings have important implications for our understanding of protective 38 immunity against SARS-CoV-2, the use of immune plasma as a therapy, and the development of 39 much-needed vaccines. 40 41

Histoplasma capsulatum, an environmental fungus, is the most common endemic pulmonary mycosis in the USA. Disease is most frequently observed in immunocompromised patients living in endemic areas. We present the mechanisms of fungal recognition, innate immune response and adaptive immune response that lead to protection or exacerbation of disease. Current understanding of these mechanisms is the result of a continuing dialogue between clinical observations and murine studies. Mice are a powerful model to study the immune response to H. capsulatum alone or in the presence of immunomodulatory drugs. Vigilance for histoplasmosis should be exercised with novel immunosuppressive agents that target the important immune pathways identified here.