Immune Cells Located in Skin Prevent and Defend Against Parasite Infections
03 Aug 2015

After infection with leishmaniasis, the skin retains a population of T cells that remember how to respond and fight previous infections, according to a new study from the University of Pennsylvania School of Veterinary Medicine. This is the first time that a group of T cells have been found to reside in a tissue in response to a parasite infection.

"The mouse is a good model as they can be infected with the same parasites that infects people and dogs, and in the wild rodents are a natural reservoir of the infection. The course of infection mimics to a large extent what happens with patients," senior author Phillip Scott, vice dean for research and academic resources and professor of immunology at the University of Pennsylvania, told ALN exclusively.

Leishmaniasis, transmitted by sand flies, causes skin ulcers that can lead to disfiguring tissue damage.

T cells detect and fight invaders in the body. They can do this either directly, through CD8 T cells, or indirectly by enlisting the help of other immune cells, through CD4 T cells.

The study showed that trasferring CD4 T cells from a mouse that had previously contracted and recovered from leishmania to a mouse that had never been infected offered partial protection from the infection. This prompted the researchers to hypothesize that type of resident memory CD4 T cell was needed.

They then looked at mice that had recovered from leishmaniasis. They found that leishmania parasite specific T cells were present throughout the skin of these mice, even in sites far away from the initial infection.

To determine whether these memory cells were in fact present in the skin and not just circulating, the team transferred skin grafts of recovered mice to mice that had never been infected. The memory CD4 cells were present in the grafts for at least four weeks, confirming that the cells were resident.

These findings may pave the way for a leishmaniasis vaccine. "There are no vaccines for human leishmaniasis, and our results suggest that developing a good vaccine may require generating T cells that can be resident in the skin.  We — and others- are now working on ways this might be done," Scottt said.