CD1 (
cluster of differentiation 1) is a family of
glycoproteins expressed on the surface of various human
antigen-presenting cells
An antigen-presenting cell (APC) or accessory cell is a cell that displays antigen bound by major histocompatibility complex (MHC) proteins on its surface; this process is known as antigen presentation. T cells may recognize these complexes using ...
. They are related to the
class I MHC
MHC class I molecules are one of two primary classes of major histocompatibility complex (MHC) molecules (the other being MHC class II) and are found on the cell surface of all nucleated cells in the bodies of vertebrates. They also occur on plat ...
molecules, and are involved in the presentation of
lipid antigens to
T cells. However their precise function is unknown.
Types
CD1 glycoproteins can be classified primarily into two groups which differ in their lipid anchoring.
* CD1a,
CD1b and
CD1c (
group 1 CD1 molecules) are expressed on cells specialized for antigen presentation.
*
CD1d (group 2 CD1) is expressed in a wider variety of cells.
CD1e is an intermediate form, expressed intracellularly, the role of which is currently unclear.
In humans
Group 1
Group 1 CD1 molecules have been shown to present foreign lipid antigens, and specifically a number of mycobacterial cell wall components, to CD1-specific T cells.
Group 2
The natural antigens of group 2 CD1 are not well characterized, but a synthetic glycolipid, alpha-galactosylceramide, originally isolated from a compound found in a marine sponge, has strong biologic activity.
Group 2 CD1 molecules activate a group of T cells, known as
Natural killer T cells because of their expression of NK surface markers such as
CD161. Natural Killer T (NKT) cells are activated by CD1d-presented antigens, and rapidly produce Th1 and Th2 cytokines, typically represented by interferon-gamma and IL-4 production.
The group 2 (CD1d) ligand alpha-galactosylceramide is currently in phase I clinical trials for the treatment of advanced non-hematologic cancers.
Diagnostic relevance
CD1 antigens are expressed on cortical
thymocytes, but not on mature T cells. This often remains true in
neoplastic cells from these populations, so that the presence of CD1 antigens can be used in diagnostic
immunohistochemistry
Immunohistochemistry (IHC) is the most common application of immunostaining. It involves the process of selectively identifying antigens (proteins) in cells of a tissue section by exploiting the principle of antibodies binding specifically to an ...
to identify some
thymomas and malignancies arising from T cell precursors. CD1a, in particular, is a specific marker for
Langerhans cells, and can therefore also be used in the diagnosis of
Langerhans cell histiocytosis. Other conditions that may show CD1 positivity include
myeloid leukaemia and some B cell
lymphomas.
In cows and mice
Mice
A mouse ( : mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus' ...
lack the group 1 CD1 molecules, and instead have 2 copies of
CD1d. Thus, mice have been used extensively to characterize the role of CD1d and CD1d-dependent
NKT cells in a variety of disease models.
It has recently been shown that
cows lack the group 2 CD1 molecules, and have an expanded set of group 1 CD1 molecules.
Because of this and the fact that cows are a natural host of
Mycobacterium bovis, a pathogen in humans as well, it is hoped that studying cows will yield insights into the group 1 CD1 antigen-presenting system.
References
External links
*
Mouse CD Antigen Chart
{{Clusters of differentiation
Clusters of differentiation