Macrophages induce antibody-dependent cytostasis but not lysis in guinea pig leukaemic cells

Effects of L2C leukemia on macrophage-mediated responses

Preliminary experiments have suggested that guinea pig L2C B-cell leukemia cells were able to evade macrophage-mediated lysis. To determine whether the L2C cells were resistant to macrophage cytotoxic activity or whether factors associated with the L2C leukemia contributed to a generalized inhibition of macrophage cytotoxic activity, pulmonary macrophages from strain 2 guinea pigs with L2C leukemia were tested for their ability to lyse the susceptible K562 cell line after activation by lipopolysaccharide (LPS) or lymphokines. In addition, the potential presence of soluble inhibitors of macrophage tumoricidal activity in serum-free culture supernatants and in serum from strain 2 guinea pigs terminally ill with the leukemia was tested by determining the effects of leukemic guinea pig serum (LGPS) or L2C-conditioned medium (CM) on the tumoricidal activity of normal pulmonary macrophages. Macrophages from guinea pigs terminally ill with L2C leukemia were demonstrated to be depressed in their cytotoxic activity against the K562 cell after stimulation by either LPS or lymphokines when compared to normal macrophages. The lymphokine-stimulated cytotoxic activity of normal macrophages was inhibited in the presence of LGPS or CM. Oxidative burst activity of normal macrophages, as measured by zymosan-stimulated production of superoxide and hydrogen peroxide, was also inhibited under these conditions. The data presented here suggests that soluble factors associated with L2C leukemia cells can suppress oxidative burst activity of macrophages in vitro and that this effect may contribute to the ability of the leukemia cells to evade macrophage-mediated cytotoxicity.

Further studies on the differences in cytotoxicity of human peripheral blood monocytes and bronchoalveolar macrophages for cultured human lung cells

Previously reported differences between the cytostatic activity of human peripheral blood monocytes (PBM) and bronchoalveolar macrophages (BAM) for cultured human lung tumor cells have been further investigated. The differences are both quantitative and qualitative and are shown not to be due to the respective methods of purification. There was a varying contribution of cytolysis to the cytostasis detected by the 75selenomethionine post-labeling assay used. Bronchoalveolar macrophages were cytolytic when tested at both low and high E:T ratios but PBM were only cytolytic at the low E:T ratio. A variable dependence upon soluble cytostatic factor(s) was suggested, and there was evidence of heterogeneity in the factors released by the two populations. Cytostatic factor production by both populations appeared to be under similar regulatory constraints. In vitro maturation of PBM altered their cytostatic dose-response curve to one resembling that previously reported for BAM. It was also shown that sera from poor-prognosis lung tumor patients, which suppressed the in vitro maturation of PBM, also suppressed the in vitro cytostatic activity of PBM for cultured human lung tumor cells.

Mechanisms of tumour cell escape encountered in treating lymphocytic leukaemia with anti-idiotypic antibody

Four patients with chronic lymphocytic leukaemia were treated by one or more infusions of polyclonal antibody specific for the immunoglobulin idiotype expressed on their leukaemic cells. The antibody was in the form of IgG from sheep antiserum. Three of the 4 cases showed a significant fall in blood lymphocyte count. On one occasion most of the residual circulating lymphocytes were apparently dead. However on all occasions the cell counts rebounded to near pre-infusion levels within one week. Viable lymphocytes recovered from the blood after infusion always showed evidence of antigenic modulation: a diminished level of surface idiotype in a patched distribution, with an accompanying refractoriness to lysis by anti-idiotype plus complement. When cultured in vitro blood lymphocytes from three of the four patients revealed an appreciable export of idiotypic Ig. These 3 patients showed plasma levels of idiotypic Ig up to 400 micrograms ml-1, reduced by plasma exchange prior to infusion. The fourth patient had a level of less than 4 micrograms ml-1, and was the only one in whom free antibody could be found in the plasma after infusion. These cases demonstrate two major factors which thwart antibody attack on leukaemic cells--extracellular antigen and antigenic modulation--as well as problems relating to sparseness of surface antigen, recruitment of effectors, and exhaustion of effectors.