The levels of expression of histocompatibility antigens on the cell membrane and their gene expression in non-metastatic and in highly metastatic Friend leukemia cells (FLC) were measured and the levels of expression of these antigens were correlated with the different in vivo behaviour of the tumor cells. Highly metastatic in vivo passaged FLC (either interferon-sensitive 745 or interferon alpha/beta-resistant 3Cl-8 cells) expressed higher levels of class I H-2K and H-2D antigens on their cell membrane with respect to the non-metastatic in vitro passaged counterparts. The increased expression of H-2 class I antigens was associated with an increased transcription of H-2K and H-2D genes. As both in vitro and in vivo passaged FLC have been shown to be resistant in vitro to the natural killer (NK) cell activity, we tried to correlate the levels of expression of histocompatibility antigens with the in vivo clearance of [125I]UDR-labeled FLC. However, no correlation was found between the levels of expression of H-2 antigens and the in vivo clearance of tumor cells. In fact, in vivo passaged FLC (tested either after 1 or after 15 in vitro passages) expressed virtually identical levels of H-2 antigens; however, the freshly explanted in vivo passaged FLC exhibited markedly lower levels of clearance from the lung, spleen and liver (when injected i.v. in DBA/2 mice) with respect to the corresponding FLC cultivated for several passages in vitro. Pretreatment of in vitro passaged 745 FLC with either interferon alpha/beta or interferon gamma resulted in the acquisition of some metastatic potential of FLC to the liver when interferon-treated FLC were subsequently injected i.v. in DBA/2 mice; such in vitro treatments resulted in a 2-3-fold increase in the expression of H-2K antigens versus the control untreated FLC. We suggest that such increases could represent some advantages for the homing properties of tumor cells and/or for the tumor progression, by mechanisms different from the resistance to the NK cells.

Animals↗

PubMedDate not supplied

[Recent data on the immunology of tumors. Mechanisms of escape of immunological control. Role of suppressor cells].

Cells in spleens from tumor bearing animals were found to inhibit in vitro reactivity of lymphocytes to a variety of stimulants. These suppressor cells inhibited the stimulation of normal lymphocytes by mitogens : P.H.A.-Con A-L.P.S. They were adherent cells, bore immunoglobulins at their surface and did not bear the 0 marker. They were also demonstrated in T deprived tumor bearing animals. They might be B cells, or, more probably, macrophages. Other activities that are inhibited by the suppressor cells are: -reactivity to allogenic cells in the mixed lymphocyte culture, -in vitro generation of secondary anti tumor cytotoxic effector cells, -macrophage migration inhibition in the presence of immune lymphocytes and tumor extracts, -reactivity against syngeneic tumor cells or tumor extracts. Suppressor cells may play a role in the general immunodepression of tumor bearing hosts, and in the inability of tumor bearing hosts to reject the tumor. However, the biological role of these non T suppressor cells is not clear, as they also inhibit tumor cell growth, and in vivo experiments favour suppressor cells of thymic origin.

Animals↗