CD4 and COVID-19: There is also evidence that monocyte and T cell subsets are involved in the pathogenesis of post-COVID-19 ILD; a recent study evaluating blood samples from subjects with post-COVID-19 ILD, IPF, and controls showed that survivors of post-COVID-19 ILD had higher expression of genes related to naïve and memory CD4 T cells, Tregs, memory CD8 T GZMB+, memory CD8 T GZMK+, and naïve CD8 T cells, but lower levels in IPF, suggesting most subjects with post-COVID-19 ILD have partially or completely resolved pulmonary fibrosis, while most patients with IPF have progressive disease (43).