CD19 and common variable immunodeficiency: In a proportion of CVID patients, an observable B cell maturation defect with reduced switched memory B cell development is also associated with expansion of transitional CD19+CD38hiIgMhi and CD21 positive B cells or more immature B cell subset with low expression of CD21 maturation marker [33, 34], which correlated with clinical phenotypes such as lymphadenopathy and splenomegaly as well as autoimmune cytopenias [35].