**5. Effect of phycocyanin on differentiation of human myeloid leukemia cell lines**

A study of aerosolized GM-CSF demonstrated tolerance and possible efficacy in patients with malignant metastases to the lungs, possibly through upregulation of antigen-specific cytotoxic T-cells (Rao et al., 2003). It is known that various food compounds and the metabolites involving phycocyanin can influence the processes in cellular differentiation, apoptosis, and proliferative potential, and there is considerable evidence that vitamins and micronutrients are able to regulate gene expression of cancer cells, resulting in influence on the carcinogenic process (Sacha et al., 2005). All-trans-retinoic acid and vitamin D3 are known as one of the physiologic agents which can modulate the proliferation and differentiation of hematopoietic cells (Collins, 2002). The vitamin plus interferon-γ (IFNγ) treatment and enrichment with polyunsaturated fatty acids such as arachidonic acid, eicosapentaenoic acid or docosahexaenoic acid also significantly enhanced immunoregulatory effects, or enhanced the expression of monocytic surface antigens CD11b and CD14 on human premonocytic U937 cells (Obermeier et al., 1995). In this section, we investigated the effects of phycocyanin on differentiation and morphological and cytochemical changes of human myeloid leukemia cell lines, U937 and HL-60 cells, generally used for the studies of cell differentiation.

A human hematopoietic cell line, U-937, was derived from a patient with generalized histiocytic lymphoma. The histiocytic origin of the cell line was shown by its capacity of lysozyme production and the strong esterase activity (naphtol AS-D acetate esterase inhibited by NaF) of the cells (Sundstrom and Nillson, 1976). The cell line was morphologically identical to that of the tumor cells in the pleural effusion, and is known to be functionally differentiated to phagocytic macrophage by cytokines from lymphocytes (Koren et al, 1979).

A continuous human myeloid cell line, HL-60, was derived from the peripheral blood leukocytes of a patient with acute promyelocytic leukemia and established. The predominant cell type is a neutrophilic promyelocyte with prominent nuclear/cytoplasmic asynchrony (Gallangher et al., 1979). HL-60 cells lack specific markers for lymphoid cells, but express surface receptors for Fc fragment and complement (C3), which have been associated with differentiated granulocytes. They exhibit phagocytic activity and responsiveness to a chemotactic stimulus commensurate with the proportion of mature cells.
