Immunopathogenesis of SARS-CoV-2 infection

National Institute Of Allergy And Infectious Diseases

Investigators

Linked publications, trials & patents

Abstract

The aim of this project is to test the hypothesis that specific chemokines and chemokine receptors drive either immunopathology or immune control of SARS-CoV-2 infection in a mouse model. The motivation for this aim is that chemokines regulate leukocyte trafficking and covid-19 disease pathogenesis involves severe immunopathology in the lung dependent on leukocyte influx. We are using huACE2 transgenic mice on a C57BL/6 background infected with the Wuhan strain of the virus as well as non-huACE2 mice infected with the MA-10 mouse adapted strain of the virus. Our goal is to test a WT LD50 dose first, screening for receptor knockouts that increase survival, since any positive results will have translational potential. Receptors that screen negative will be rescreened at an LDzero looking for protective chemokine receptors in the model. Both females and males will be tested and are expected to have differences in clinical progression of coronaviral disease and histopathology, based on other infectious disease models in mice, and differences between the sexes observed in humans infected with SARS-CoV and SARS-CoV-2. In all subsequent experiments, clinical disease progression will be assessed by virus recovery from throat swabs, blood and stool; serum antibody titers, hemograms, blood chemistries and serum cytokines before and at multiple intervals after infection; as well as physical appearance, weight loss, and progression to moribundity and survival for a month after infection. Animals will be euthanized by CO2 and cervical dislocation at the latest one-month post-infection. In our experience, to observe significant differences in survival we will need 20 mice/cohort in each experiment and repeat the experiment 3 times due to the variance in survival between experiments. These numbers should be sufficient to observe significant differences in the other clinical data as well. Fewer non-infected mice will be needed since there is expected to be less variance among these controls. In this reporting period, the results of our ko screen has revealed protective effects of Ackr1 deficiency and harmful effects of Ccr2, Ccr5 and Cxcl10 deficiency. A secondary goal is to characterize the local immune response in cultured human lung explants infected with SARS-CoV-2. We have succeeded in collaboration with L Margolis from NICHD in establishing this system and demonstrating productive infection in epithelial cells. In FY23, we reported that atypical chemokine receptor 1 (Ackr1, also known as Duffy antigen receptor for chemokines/DARC) was the most highly upregulated chemokine receptor in infected lung, where it localized to endothelial cells of veins and arterioles. In a screen of 7 leukocyte chemoattractant or chemoattractant receptor knockout mouse lines, Ackr1-/- mice were unique in having lower mortality after SARS-CoV-2 infection, particularly in males. ACKR1 is a non-signaling chemokine receptor that in addition to endothelium is also expressed on erythrocytes and Purkinje cells of the cerebellum. It binds promiscuously to both inflammatory CC and CXC chemokines and has been reported to control chemokine availability which may influence the shape of chemotactic gradients and the ability of leukocytes to extravasate and produce immunopathology. Of note, erythrocyte ACKR1 deficiency is fixed in sub-Saharan African populations where COVID-19 has been reported to result in low mortality compared to worldwide data. Our data suggest the possibility of a causal contribution of ACKR1 deficiency to low sub-Saharan COVID-19 mortality and identify ACKR1 as a possible drug target in the disease.