Macroautophagy and cell death both contribute to innate immunity, but little is known about how these processes integrate. Drosophila larval salivary glands require autophagy for developmentally programmed cell death, and innate immune signaling factors increase in these dying cells. Here, we show that the nuclear factor kappaB (NF-kappaB) factor Relish, a component of the immune deficiency (Imd) pathway, is required for salivary gland degradation. Surprisingly, of the classic Imd pathway components, only Relish and the PGRP receptors were involved in salivary gland degradation. Significantly, Relish controls salivary gland degradation by regulating autophagy but not caspases. In addition, expression of either Relish or PGRP-LC causes premature autophagy induction and subsequent gland degradation. Relish controls autophagy by regulating the expression of Atg1, a core component and activator of the autophagy pathway. Together these findings demonstrate that a NF-kappaB pathway regulates autophagy during developmentally programmed cell death.

Several types of cell death including apoptosis, necroptosis and autophagic cell death play diverse roles in different biological processes. In addition to its essential roles in development and metabolism, programmed cell death is indispensable for host immunity. Interestingly, current research shows that these processes are connected but the nature and extent of the crosstalk between host defense and programmed cell death still remains an area of great interest. The NFkB factor Relish is best characterized as a crucial component of Drosophila Imd pathway, which generates immune responses by producing antimicrobial peptides following Gram-negative bacterial infection. In this dissertation, I demonstrate a novel role of Relish in developmentally programmed cell death. During metamorphosis, Drosophila salivary glands are degraded by the collective actions of caspase-dependent and autophagic cell death. Here I show that Relish mutants displayed improper salivary gland degradation and the persistence of salivary gland cell fragments. Expression of Relish in salivary glands rescued this phenomenon. Among the upstream components of the Imd pathway, mutants in the bacterial peptidoglycan receptors, PGRP-LC and-LE also exhibited similar defects in gland degradation, but surprisingly none of the other Imd pathway components examined had any such effect. As both Relish and PGRPs are critical for host defense against bacterial infection, our next concern was the role of host microflora in salivary gland degradation. However, observation of normal salivary gland cell death in axenic flies ruled out the possible involvement of microbiota. Robust genetic analyses proved that Relish-mediated cell death occurs in caspase-independent but autophagy-dependent manner. Moreover, expressions of either active version of Relish or PGRP-LC resulted in the premature gland degradation and induction of autophagy. Finally, I show that Relish controls autophagy by regulating the expression of Atg1, a core component of the autophagy pathway. Together these findings suggest the existence of a novel pathway, which connects immune response factors to developmentally programmed cell death.

The inflammatory cytokine IL-1beta is critical for host responses against many human pathogens. Here, we define Group B streptococcus (GBS)-mediated activation of the Nod-like Receptor-P3 (NLRP3) inflammasome in macrophages. NLRP3 activation requires GBS expression of the cytolytic toxin, beta-hemolysin, lysosomal acidification, and leakage. These processes allow the interaction of GBS RNA with cytosolic NLRP3. The present study supports a model in which GBS RNA, along with lysosomal components including cathepsins, leaks out of lysosomes and interacts with NLRP3 to induce IL-1beta production.