The findings provide unexpected insights into how immune cells are regulated in the brain and have implications for treatment of any inflammatory condition that affects the brain.

Toxoplasma, a common parasite of humans, is found in the brains of approximately 30 percent of the population. Yet, because the brain lacks its own lymphatic system for localized immune response and the blood brain barrier limits antibody entry, researchers have found it provides unique challenges for the immune system to control local infection. Therefore, little is known about the processes by which T cells access the central nervous system during toxoplasma infection or how the immune system keeps this parasite in check.

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To understand lymphocyte behavior in the brain, we used two-photon microscopy to visualize effector CD8+ Tcells during toxoplasmic encephalitis. These cells displayed multiple behaviors with two distinct populations of cells apparent: one with a constrained pattern of migration and one with a highly migratory subset. Credit: Chris Hunter, University of Pennsylvania

"We found, quite unexpectedly, that the movement of infiltrating T cells was closely associated with an infection-induced reticular system of fibers in the brain," lead author Emma Wilson said. "These structures were not present in normal brain tissue."

"This observation suggests that in the brain, specialized structures are induced by inflammation that guide migration of T cells in this immune-privileged environment and allow them to perform a search-and-destroy type of mission required to find abnormal cells or microbes with the brain," Hunter, professor and chair of the Department of Pathobiology at Penn Vet, said.

Source: University of Pennsylvania