Effect of different immune priming doses on survival after secondary challenge with live bacteria in Drosophila melanogaster

Abstract

Invertebrates rely solely in innate immunity, which is believed to always respond to an infection the same way. However, in recent work, phenomenological evidence has been found in arthropods, suggesting that the innate immune system might also provide immune memory under some circumstances, the socalled ‘immune priming’. However, immune priming in arthropods is not fully understood and evidence to support such a phenomenon is not always found. Here I argue that we do not have a very good understanding of some of the basic aspects of these experiments and that many experimental parameters can be adjusted when testing for such a phenomenon, for example, the first dose of parasite that an individual receives (priming dose) before the secondary dose (challenge), to test for a priming effect. In this thesis I used D rosophila melanogaster as a host and the bacteria L actococcus lactis as pathogens to try to (i) estimate the 50% lethal dose after 7 days, and to answer whether (ii) we find evidence of immune priming in terms of increased survival after secondary challenge?, (iii) are responses affected by priming dose of heatkilled bacteria? and (iv) if there is priming, is it affected by whether the priming dose is of live or dead bacteria? We have demonstrated that flies can present a significant higher survival after a secondary challenge of live bacteria when previously primed with a different doses of heatkilled and live bacteria, but in an overall view, it is still early to affirm that this response could be due to a priming effect, since the increase in the survival rate was small. This experiment highlights the necessity of more investigation is this field, exploring other parameters as time between priming and challenge, different priming doses and interaction of D rosophila with other bacteria.