U937 is a human monocytic cell line obtained from histiocytic lymphoma. A histocyte is a cell that is part of the mononuclear phagocytic system that takes part in the immune responses. These are typically derived from the bone marrow. Being monocytic in nature, U937’s secrete cytokines, chemokines and other extracellular mediators under stimulation.

U937 cells were first isolated from a 37 year old male patient for the cells to be used in properties of differentiation of monocytes. The results obtained showed that the U937 cells were able to differentiate under a variety of stimulus. Tissue culture cellular studies have shown that combinations of vitamin D derivatives and retinoids such as ATRA and 9-cis retinoic acid show cooperative effects on differentiation in established leukemia cell lines U937 cells.

In addition, U937cells have also been induced to differentiate by treating then withall-trans-retinoic acid, dimethyl sulfoxide, and lymphokine. Differentiation has been shown by changes in morphology, certain cytochemical enzymes and the expression of macrophage markers.

The U93 cell line is an extensively used cell line in Tissue Culture labs allowing their properties to be used as a monocyte capable of differentiating into macrophages. One major characteristics of U937 cells is the expression of 44-46 kDa paxillin forms under the stimulation of IFN-beta and IFN-gamma. Paxillin is an adhesion-associated protein containing phosphotyrosine that plays a role in several signaling pathways.

James SY, Williams MA, Newland AC, Colston KW. 1999. Leukemia cell differentiation: cellular and molecular interactions of retinoids and vitamin D. Gen Pharmacol. 1999 32:143-54