Results indicate that the midgut of Stomoxys calcitrans possesses antiGram-positive bacteriocidal activity. The main activity was found in the anterior midgut. The activity was inducible on blood feeding and enhanced by Lipopolysaccharide feeding in a dose dependent manner.
Ultrastructural study revealed that after ingestion, LPS interacts with the plasma membrane of the reservoir zone of the midgut and acts on subcellular structures. This results in changes in the morphology of the organelles that presumably lead to changes in the cellular activities resulting in induction of a local immune response in the reservoir region of S. calcitrans.
SDS-PAGE analysis generated too many protein bands from S. calcitrans. This was possibly because of shearing of bacteria during protein extraction, and was consequently unable to detect Gram positive bacteria binding protein.
Southern blot analysis revealed that the genome of the S. calcitrans contains diptericin as a single copy gene. In further investigation, I did not manage to clone diptericin from the genomic library or midgut specific cDNA library of S. calcitrans.
Results of Southern blot analysis showed that S. calcitrans contains two copies of both the Stomoxys midgut defensin 1 (Smd1) and Stomoxys midgut defensin 2 (Smd2) genes. Northern blot analysis revealed that both these defensin molecules are constitutively expressed in the reservoir region of S. calcitrans and are upregulated by artificial blood and blood meal plus LPS but their expression was not detected in the fat body tissues. Northern analysis further showed that the cAMP signaling pathway does not have a direct influence on transcriptional levels of midgut defensin genes in S. calcitrans. Furthermore, no expression of Smd1 and Smd2 was detected in the developmental stages of S. calcitrans i.e. from egg to pupa.