Drosophila larval fat body surfaces : Changes in transplant compatibility during development

The hemocytes oftu-Sz ^ts melanotic tumor larvae ofDrosophila melanogaster encapsulate heterospecific and surface-modified homospecific tissue implants, but do not encapsulate unmodified homospecific implants (R. Rizki and Rizki 1980). In the present study we usedtu-Sz ^ts hosts to assay changes in larval fat body surfaces during development. Donor fat bodies from various ages of larvae were accepted (remained unencapsulated) intu-Sz ^ts hosts whereas fat bodies from donors with everted spiracles and all subsequent stages of development that were tested were rejected (encapsulated). Since the demarcation between acceptance and rejection by thetu-Sz ^ts blood cells did not coincide with the gross morphological changes that appear in the fat body during metamorphosis (dissolution of the basement membrane and dispersal of the freed fat body cells at pupation), we compared acceptable and nonacceptable fat body surfaces by three other methods. Fat body surface ultrastructure was examined, fat bodies were treated with fluorescein isothiocyanate-conjugated lectins, and fat body surfaces were reacted with a monoclonal antibody specific for basement membrane. These approaches did not uncover fat body surface changes associated with eversion of the anterior spiracles, suggesting that recognition of tissue surface heterogeneities by the insect hemocytes exceeds the resolving power of the other three methods. However, the monoclonal antibody fails to bind to the basement membrane ofD. virilis larvae, whose fat body is always rejected intu-Sz ^ts hosts. This supports our suggestion that the molecular architecture of the basement membrane may be important in eliciting the encapsulation response.