Age-associated mortality in immune challenged mosquitoes (Aedes aegypti) correlates with a decrease in haemocyte numbers

Abstract

SummaryMosquitoes vector pathogens. One aspect that has been overlooked in mosquito-pathogen relationships is the effect of host age on immune competence. Here, we show that there is age-associated mortality following immune challenge with Escherichia coli . This mortality correlates with a decrease in haemocyte numbers (blood cells) and a decreased ability to kill E. coli . Although the number of haemocytes decreases, the available haemocytes retain their phagocytic ability regardless of age, and we estimate that individual granulocytes can phagocytose approximately 1500 E. coli . Moreover, transcription profiles for cecropin, defensin and gambicin in E. coli challenged mosquitoes do not change with age, indicating that the increased susceptibility is not attributed to fewer humoral antimicrobial peptides. These results suggest that a contributing factor for the age-associated mortality is the decrease in circulating haemocytes, which reduces the overall phagocytic capacity of mosquitoes. To our knowledge, this is the first report detailing an age-associated decline in the immunological capabilities of mosquitoes following challenge with an infectious agent. These data also call for caution in the analysis and interpretation of experimental results when mosquito age has not been closely monitored. Lastly, a model for haemocyte function is presented.

Clone-specific immune reactions in a trematode-crustacean system

“…However, the increase observed here contrasts with other studies showing a decrease in THC (Hillyer et al 2005;Cornet et al 2009) and still others showing an initial decrease followed by a return to prior levels (Persson et al 1987;Lorenzon et al 1999). This discrepancy can be attributed to a number of possible factors.…”

Adult honeybees (Apis mellifera L.) abandon hemocytic, but not phenoloxidase-based immunity

“…Nevertheless, hemocyte loss in adult honeybees might be regulated by endocrine factors. Age-related hemocyte loss has been recorded in other insect species (Hillyer et al, 2005;Stanley and Park, unpublished data). For one example, Stanley and Park (unpublished data) recorded a steady decline in hemocyte populations in adult males of the cricket Gryllus firmus beginning after they reached the age of 3 weeks.…”

Senescence of the cellular immune response in Drosophila melanogaster

“…In scorpion flies (Panorpa vulgaris), whilst haemocyte numbers remained unchanged during ageing, the phagocytic activity of those cells declined [23]. Hillyer et al, [24] showed that older mosquitoes (Aedes aegypti) had reduced survival following infection with E. coli, a lower ability to clear the infection, and [5] fewer phagocytic haemocytes compared with younger mosquitoes. However they only assayed mosquitoes across the first five days of life, so it is questionable whether these trends truly represent senescence or some other life-history shift.…”