Blood cell surface changes in Drosophila mutants with melanotic tumors.

When wheat germ agglutinin conjugated to fluorescein isothiocyanate is bound to hemocytes from larvae of Drosophila melanogaster, two populations of hemocytes are distinguished. One shows a fluorescent speckled surface (spk+) and the other lacks this characteristic (spk-). In mutant larvae with melanotic tumors and in larval hosts with heterospecific implants, most of the lamellocytes (a hemocyte variant involved in capsule formation and tissue rejection) are spk+, whereas the lamellocytes in nontumorous larvae are spk-. This suggests that spk+ lamellocytes are necessary for encapsulation of aberrant tissues in the mutant larvae and are responsible for rejection of foreign tissue implants.