Lectin-induced cytotoxicity of unprimed mouse spleen cells to allogeneic and xenogeneic target cells

To analyze the differential lysis of target cells by ConA and PHA-activated cytotoxic cells, two possibilities were considered: (1) resistance or sensitivity of the target to lysis was a property of the target cells, (2) ConA and PHA could be activating different antigenic structures. The density of ConA receptors on the three cell lines was determined in an effort to test the first possibility. Results showed that K562 cells which are not lysed by ConAactivated cells do have a low density of ConA receptors when compared to the other two cell lines. However, L cells which are also not lysed by ConA-activated cytotoxic cells possess a density of ConA receptors comparable to YAC cells which are targets. Therefore, a correlation between target cell resistance to lysis and diminished density of ConA receptors could not be made.

Cold target inhibition studies were done in an attempt to determine the specificity of ConA and PHA activated cells. A statement regarding the specificity of the lectin response could not be made based on the data obtained from the above studies. In this regard, two lines of evidence suggest that different subpopulations of effectors may be responding to induction by the two lectins (possibility 2). First, competition for effector cells did not occur when both lectins were included in the assay. Second preliminary data using anti la sera and complement suggest that ConA and PHA activate different cells.

Membrane separation experiments and wash and media change techniques indicate that the mediation of cytotoxicity by ConA-activated cells do not involve soluble factors. Mediation of cytotoxicity in the PHA system may involve such factors.

It was noted that the development of cytotoxic effector cells may be independent of proliferation and most of macromolecular synthesis.

Requirements for activation of cytotoxic cells: (1) responsible cells were T cells; (2) the incubation period by lectin was greater than 8 hours; (3) there was a limited range of effective lectin concentrations; (4) reduction of macrophages to 1% of cell population did not affect lectin activation of cytotoxicity; (5) immunoglobulin-bearing cells are not involved.