Researchers Discover a New Gatekeeper Role for Thymic Dendritic Cells in Controlling T Cell Release into the Bloodstream

T lymphocytes are blood cells that carry out the main functions of our immune system. Dendritic cells and B lymphocytes are other types of immune cells that present foreign substances (such as microbial proteins) and “self” substances from our own tissues to T lymphocytes. In this way, T lymphocytes are “educated” to distinguish between self and non-self, so they can mount an immune response to pathogens but recognize and remain tolerant of one’s own bodily tissues. When this system fails to operate properly, autoimmune disease and immune deficiencies can result. T lymphocytes undergo maturation in the thymus, a small gland located just above the heart, and are then released into the bloodstream. T lymphocyte egress from the thymus is essential for immune surveillance and to fight various types of infections. Sphingosine-1-phosphate (S1P) is a lipid molecule found at high levels in the blood and low levels in most tissues. Mature T cells produce a cell surface receptor that recognizes S1P, allowing the S1P chemical gradient to attract them into the bloodstream once they have completed their education in the thymus. However, the precise mechanisms that control T lymphocyte egress are not fully understood.

Thymic dendritic cells have a well-established role in antigen presentation and immune tolerance in the body. In addition to this role, dendritic cells also act as metabolic gatekeepers of lymphocyte trafficking. The team showed that thymic dendritic cells take up S1P, a blood borne lipid mediator, and metabolize it through the actions of an enzyme called S1P lyase, generating a localized S1P gradient that facilitates T lymphocyte egress into the blood In light of the fact that dendritic cells are known to continually traffic throughout the body surveying for the presence of infectious agents, the team’s observations raise the possibility that dendritic cells could potentially control the release of T lymphocytes in response to various disease states or conditions. These findings provide a deeper understanding of how the body regulates lymphocyte trafficking.

“T cells are needed to orchestrate the body’s immune response against pathogenic organisms and also against cancer cells,” says UCSF Benioff Oakland’s Dr. Julie Saba, one of the study’s authors. “In addition to natural T cells, genetically engineered T cells are being used in revolutionary ways to treat cancer. However, conditions such as chronic infection, aging, cancer and bone marrow transplantation can reduce T cell output from the thymus, compromising immune function. By learning what controls T cell output, we hope to be able to restore T cell production when it is low and provide more T cells for therapeutic purposes. ”

In addition to Saba, other co-authors are Jesus Zamora-Pineda, Ashok Kumar, Jung H. Suh, and Meng Zhang,

The research is supported by the (CA129438) and Swim Across America funds (to J.D. Saba). Confocal images were acquired at the Children's Hospital Oakland Research Institute Microimaging Facility supported by an NIH grant (S10RR025472) and the Children's Hospital Branches, Inc. S1P measurements were obtained using the Children's Hospital Oakland Research Institute Mass Spectrometry Facility supported by an NIH Health grant (S10OD018070).

About UCSF Benioff Children’s Hospital OaklandUCSF Benioff Children’s Hospital Oakland (formerly Children’s Hospital & Research Center Oakland) is a premier, not-for-profit medical center for children in Northern California, and is the only hospital in the East Bay 100% devoted to pediatrics. UCSF Benioff Children’s Hospital Oakland affiliated with UCSF Benioff Children’s Hospital San Francisco on January 1, 2014. UCSF Benioff Children’s Hospital Oakland is a national leader in many pediatric specialties including cardiology, hematology/oncology, neonatology, neurosurgery, endocrinology, urology, orthopedics, and sports medicine. The hospital is one of only five ACS Pediatric Level I Trauma Centers in the state, and has one of largest pediatric intensive care units in Northern California. UCSF Benioff Children’s Hospital Oakland is also a leading teaching hospital with an outstanding pediatric residency program and a number of unique pediatric subspecialty fellowship programs.

UCSF Benioff Children’s Hospital Oakland’s research arm, Children’s Hospital Oakland Research Institute (CHORI), is internationally known for its basic and clinical research. CHORI is at the forefront of translating research into interventions for treating and preventing human diseases. CHORI has 250 members of its investigative staff, a budget of about $50 million, and is ranked among the nation’s top ten research centers for National Institutes of Health funding to children’s hospitals. For more information, go to www.childrenshospitaloakland.org and www.chori.org.