CD4 and synovitis: Flow cytometric analysis of mice’ synovium on the 7th, 14th, and 30th day after collagenase injection could be addressed by histological findings, i.e., higher mononuclear cell infiltration (monocytes, macrophages, and CD4 T cells) corresponds to the synovial inflammation (synovitis) and newly formed blood vessels seen in the histological samples during early OA.