Purification and characterization of a human leukemia cell-derived immunosuppressive factor

Effect of tumor growth on the blastogenic response of splenocytes: a role of macrophage-derived nitric oxide

In vivo growth of Dalton's lymphoma (DL), a spontaneous T cell lymphoma, has been found to increase the count of peripheral blood leukocytes (PBL). However, bone marrow cell proliferation and differentiation remained unaffected (A. Kumar and S.M. Singh, Immunol. Cell Biol., 73, 220-225). The present investigations were undertaken to study the effect of DL growth on the blastogenic response of splenocytes. A decrease in the wet weight of the spleen and in the count of splenocytes was observed at the early DL-bearing stage which, however, increased through the mid and late stages of the tumor growth. In vitro, the blastogenic response of the splenocytes of DL-bearing mice to phytohemagglutinin (PHA) was low at the early stage of the tumor, and subsequently increased at the mid and late stages. Macrophage-derived nitric oxide (NO) was found to be involved in regulating the blastogenic response of the splenocytes. DL cells are thus shown to influence splenocyte blastogenesis by altering the NO production of splenic macrophages.

Antigens of Lyme disease of spirochaete Borrelia burgdorferi inhibits antigen or mitogen-induced lymphocyte proliferation

Modulation of cellular immune responses by the spirochaete Borrelia burgdorferi, the bacteria that causes Lyme disease, was demonstrated. When cultured in the presence of sonicated Borrelia preparation (Bb), the mitogen- or antigen-stimulated proliferative responses of normal lymphocytes were consistently lowered. Bb caused the greatest reduction in Concanavalin A (ConA) or antigen-stimulated proliferation, where almost 100% reduction in proliferation could be achieved. Bb also reduced phytohemagglutinin-M (PHA) or pokeweed mitogen (PWM)-stimulated peripheral blood lymphocyte (PBL) proliferation, with the PWM proliferation being the least affected. This regulatory activity was not due to toxicity and was determined to be caused by Bb protein antigens. The degree of the proliferation reduction was directly proportional to both Bb quantity and length of exposure to lymphocytes. IL-2 production was significantly reduced from Bb-exposed lymphocytes. The entry of lymphocytes into the proliferating phases of the cell cycle was also shown to be blocked. These results have demonstrated an immune suppressive mechanism of B. burgdorferi. The magnitude of host immune responses may be dependent on the degree of suppression which is related to the spirochaete quantity and their length of presence in the host.

Identification of a co-stimulatory factor for human T cell proliferation

A factor enhancing proliferation of human peripheral blood lymphocytes (PBL) was identified in the culture supernatant of a human myeloid cell line HL-60 after ion exchange separation. Partially purified lymphocyte growth enhancing factor (LGEF) was found to enhance mitogen-stimulated PBL or purified T cell proliferation in a dose dependent fashion. LGEF alone did not stimulate PBL or T cell proliferation and its activity was dependent on the presence of mitogen. LGEF mediated T cell proliferation was neither accompanied by an increase in the level of IL-2 receptor expression, nor was dependent on the presence of monocytes. In ELISA assay antibodies against IL-1, IL-2, IL-3 and IL-6 did not recognize the LGEF preparation. The comparison of LGEF with other lymphokines is discussed.