CD4 and osteoarthritis, knee: To study infiltrating immune cells in knee osteoarthritis, scientists found that CD14+ macrophages were the predominant cells in the synovial membrane, followed by CD4+ T lymphocytes, whereas mast cells, B cells, and plasma cells were also found, but to a lesser extent (de Lange-Brokaar et al., 2012; Deligne et al., 2015; Moradi et al., 2015; de Lange-Brokaar et al., 2016; Klein-Wieringa et al., 2016; Lopes et al., 2017; Mathiessen and Conaghan, 2017; Scanzello, 2017).