Review CD1 tetramers: a powerful tool for the analysis of glycolipid-reactive T cells Ste ´phane Sidobre, Mitchell Kronenberg * Division of Developmental Immunology, La Jolla Institute for Allergy and Immunology, 10355 Science Center Drive, San Diego, CA 92121, USA Received 10 October 2001; accepted 14 January 2002 Abstract CD1 proteins constitute a third class of antigen-presenting molecules. They bind lipids rather than peptides, and the T cells reactive to lipids presented by CD1 have been implicated in the protection against autoimmune diseases and infectious microorganisms and in the immune surveillance for tumors. Thus, the ability to identify, purify, and track the response of CD1- reactive cells is of paramount importance. Previously existing methods for identifying these T cells were not based on TCR specificity, and therefore the data obtained by these methods were in some cases difficult to interpret. The recent generation of tetramers of a-galactosyl ceramide (a-GalCer) with CD1d has already permitted significant insight into the biology of NKT cells. Tetramers constructed from other CD1 molecules also have been obtained during the previous year. Collectively, these new reagents promise to greatly expand knowledge of the functions of lipid-reactive T cells, with potential use in monitoring the response to lipid-based vaccines and other treatments and in the diagnosis of autoimmune diseases. D 2002 Elsevier Science B.V. All rights reserved. Keywords: CD1 tetramers; Lipid-reactive T cells; a-GalCer 1. Introduction CD1 proteins are cell surface glycoproteins expressed as approximately 50-kDa glycosylated heavy chains that are noncovalently associated with h2-microglobulin (h2m) (Porcelli, 1995). The human CD1 gene family contains consists of five genes, CD1A through CD1E; there are only two highly similar genes in mice, called CD1D1 and CD1D2. On the basis of their predicted amino acid sequence homologies, the members of the CD1 family can be divided into two groups (Calabi and Milstein, 2000). CD1a, -b, and -c form group I and human, mouse, rat, and rabbit CD1d form group II. Although CD1 proteins display some unique characteristics, they are distantly related to MHC class I and class II molecules, and they are considered to constitute a conserved third class of antigen-presenting molecules. CD1 proteins are encoded by genes outside the MHC locus. Unlike classical antigen-presenting molecules encoded in the MHC, they are nonpolymorphic, their surface expression does not require a functional trans- porter associated with antigen processing (TAP) (Por- 0022-1759/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII:S0022-1759(02)00204-1 * Corresponding author. Tel.: +1-858-678-4540; fax: +1-858- 678-4595. E-mail address: mitch@liai.org (M. Kronenberg). www.elsevier.com/locate/jim Journal of Immunological Methods 268 (2002) 107 – 121