SELECTIVE KILLING OF CD8(-ACETYL-D-GALACTOSAMINE-SPECIFIC LECTIN FROMVISCUM-ALBUM L() CELLS WITH A MEMORY PHENOTYPE (CD62L(LO)) BY THE N)

As reported previously by our group, among the toxic proteins from Vis cum album L. only the mistletoe lectins (MLs) induce the apoptotic kil ling pathway in human lymphocytes, Although one may expect a homogenou s distribution of carbohydrate domains on cell surface receptors for t he carbohydrate binding B chains of the toxic protein, the sensitivity of cells to these B chains obviously differ. Here we report a selecti ve killing of CD8(+) CD62L(lo) cells from healthy individuals by the g alNAc-specific ML III (and RCA(60) which binds to gal and galNAc), whi le the gal-specific ML I was less effective. This selective killing is not sufficiently explained by protein synthesis inhibition alone, sin ce this subset was not affected by other ribosome inhibiting proteins such as the lectin from Ricinus communis (RCA(120)), lectin from Abrus precatorus (APA), abrin A, and inhibitors of RNA, DNA and/or protein synthesis such as actinomycin D, mitomycin C, and cycloheximide, We co nclude that CD8(+) cells with 'memory' phenotype (CD62L(lo)) are more sensitive to the ML III-mediated killing than their CD8(+) CD62L(hi) c ounterparts, CD4(+) T cells, and CD19(+) B cells, These cells probably express a distinct receptor with galNAc domains that is missing or no t active on CD8(+) cells with a 'naive' phenotype.