My project consisted of figuring out whether blockade of IL-10 cytokine had any effect on the circadian protection of the host immune response against Influenza A virus (IAV). In our previous studies, especially the 2019 Nature Communications publication “Circadian control of lung inflammation in influenza infection”, it has been proven that circadian rhythms provide a time-of-day specific protection from mortality in Influenza A Virus (IAV) PR/8 infection that is lost in clock-disrupted mice. We have also seen that key characteristics of dawn-infected subset (ZT23) are increased levels of IL-10 and NK cells, which resulted in elevated survival rates for the dawn-infected mice against the acute viral infection. IL-10 blockade using IL-10R1α antibody was conducted to determine whether the presence of IL-10 was a main driving force behind the circadian protection of the dawn-infected (ZT23) group compared to the dusk-infected (ZT11) group. We used 10-20 weeks old C57bl6/J mice with equal male and female ratio, as well as specially designed circadian cabinets to acclimatize mice to reverse light cycling. We infected the mice at Day 0 with H1N1 PR/8 virus with 100 mg/10 µL IgG or IL-10R1α. On Days 3, 5, 6, and 9, we administered either IgG or IL-10 Ab treatments in various doses. Days 8 and 14 marked early and late harvests, respectively. After harvest, we conducted immunohistochemistry and D14 KRT5 and LAMP-3 immunofluorescence co-staining. Looking at the survival and weight loss curves, IL-10 blockade due to IL-10R1α resulted in significantly worsened survival in ZT23 group as well as more prominent weight loss. Histology images also show significantly worsened pathology for ZT23 Ab (IL-10R1α) group compared to IgG. Immunohistochemistry for CD3, marker for lymphocytes, and F4/80, marker for the myeloid population, were then conducted. ZT23 IgG control group exhibited significantly less lymphocytes compared to other groups, suggesting that increased lymphocytes in the infected region is the driving force behind severe inflammation. F4/80 is a pan-marker for dendritic cells, macrophages, monocytes, and more lineages. Therefore, F4/80 is not able to detect specific cell types to prove causality. The D14 KRT5 and LAMP-3 co-staining was a three-day process to identify which groups exhibited more KRT5 positive dysplastic areas. Upon severe lung injuries (due to Covid-19 or H1N1 PR/8), basal stem cells produce KRT5 in damaged alveolar regions instead of normal repair from AT2 cell proliferation. This causes KRT5 dysplasia which is not a normal, but an immediate repair from severe lung damages. Given this background, we have seen that ZT23 IgG control group exhibited significantly lower levels of KRT5 dysplasia, close to zero, while ZT23 Ab group exhibited similar levels of KRT5 dysplastic areas when compared to ZT11 IgG and Ab groups. This shows that IL-10 blockade results in the failure to proceed to normal cell repair and produces KRT5 pods which indicates abnormal response against severe damage. In conclusion, blockade of IL-10 signaling abrogates the time-of-day specific protection from IAV. Some future directions could be asking how other cytokine or chemokine (e.g. Interferon-gamma) levels change due to IL-10 blockade and how this relate to the magnitude of T-cell activation.