Daily <it>Plasmodium yoelii </it>infective mosquito bites do not generate protection or suppress previous immunity against the liver stage

• Main Authors: Wong Kurt A, Galan-Rodriguez Cristina, Leitao Ricardo, Pollock Tzvi, Rodriguez Ana
• Format: Article
• Language: English
• Published: BMC 2011-04-01
• Series: Malaria Journal
• Online Access: http://www.malariajournal.com/content/10/1/97

<p>Abstract</p> <p>Background</p> <p>Human populations that are naturally subjected to <it>Plasmodium </it>infection do not acquire complete protection against the liver stage of this parasite despite prolonged and frequent exposure. However, sterile immunity against <it>Plasmodium </it>liver stage can be achieved after repeated exposure to radiation attenuated sporozoites. The reasons for this different response remain largely unknown, but a suppressive effect of blood stage <it>Plasmodium </it>infection has been proposed as a cause for the lack of liver stage protection.</p> <p>Methods</p> <p>Using <it>Plasmodium yoelii </it>17XNL, the response generated in mice subjected to daily infective bites from normal or irradiated mosquitoes was compared. The effect of daily-infected mosquito bites on mice that were previously immunized against <it>P. yoelii </it>liver stage was also studied.</p> <p>Results</p> <p>It was observed that while the bites of normal infected mosquitoes do not generate strong antibody responses and protection, the bites of irradiated mosquitoes result in high levels of anti-sporozoite antibodies and protection against liver stage <it>Plasmodium </it>infection. Exposure to daily infected mosquito bites did not eliminate the protection acquired previously with a experimental liver stage vaccine.</p> <p>Conclusions</p> <p>Liver stage immunity generated by irradiated versus normal <it>P. yoelii </it>infected mosquitoes is essentially different, probably because of the blood stage infection that follows normal mosquito bites, but not irradiated. While infective mosquito bites do not induce a protective liver stage response, they also do not interfere with previously acquired liver stage protective responses, even if they induce a complete blood stage infection. Considering that the recently generated anti-malaria vaccines induce only partial protection against infection, it is encouraging that, at least in mouse models, immunity is not negatively affected by subsequent exposure and infection with the parasite.</p>