A team of researchers at the University of Rochester Medical Center has been studying proteins called integrins that enable T cells, a major subset of immune cells, to migrate. The integrin-related mechanisms described for the first time in the current paper suggest a way to shut down only those T cells currently in the act of disease-related migration, while leaving in place reserves needed in the likely event that another infection occurs during treatment. Making the mechanistic discoveries possible was a successful effort by the team to capture on video the first detailed images of fast-migrating T cells and the behavior of key proteins related to migration, which had been tagged with fluorescence. Twelve videos of T cells, and their key migration proteins, in action are part of the publication and are available online.
"There are many cases where it would be incredibly useful to precisely block integrin activation, and thus T cell migration," said Minsoo Kim, Ph.D., assistant professor of Microbiology and Immunology within the David H. Smith Center for Vaccine Biology and Immunology at the Medical Center, and lead author of the article. "Good examples include when our immune system attacks our own cells, or rejects a lifesaving transplant or clogs our blood vessels by mistake. The problem is that past, system-wide attempts that block all integrin activation, like the multiple sclerosis drug Tysabri, shut down not only unwanted inflammation in one locale, but also vital immune defenses elsewhere, leaving patients vulnerable to infection."
Kim's team found that a subset of integrins, including lymphocyte function--associated antigen-1 (LFA-1), control whether or not the tail end of the T cell can "let go" (de- adhesion). Data revealed for the first time that a protein called non-muscle myosin heavy chain-IIA (MyH9) is recruited to LFA-1 at the trailing end of migrating T lymphocytes. Experiments that interfered with the association between MyH9 and the LFA-1 integrin were found to prevent the trailing edge of the crawling T cell from letting go, dramatically reducing the ability of T cells to move. Myosins are motor proteins that expend energy to enable cell skeletons to contract.