CD proteins

Fig. 6 Transition temperature of protein unfolding measured by CE and CD. Proteins lysozyme from chicken egg (LYS), a-lactalbumin from human milk (LAL-h), a-lactalbumin type III from bovine milk (LAL-III), cytochrome c from bovine heart (CYT), recombinant dihydrofolate reductase (DHFR).

Most T helper cells express a membrane protein termed CD4 on their surface. Most T cytotoxic and T suppressor cells produce a different cell surface protein, termed CDS. Monoclonal antibodies specifically recognizing CD4 or CDS proteins can thus be used to differentiate between some T cell types. 

Some of these accessory proteins are summarized in Table 14.2. All T cells express a set of invariant transmembrane polypeptide chains, the so-called CD3 complex. CD is the abbreviation of cluster of differentiation, because each of the CD proteins was originally... 

The T-cell antigen receptor binds to the CDS protein complex at the cell membrane. A commercially available anti-CD3 antibody is polyclonal and reacts with most T-cell lymphomas in fixed tissue, the exceptions being some anaplastic large cell lymphomas and natural killer leukemia/lymphomas. CDS is specific for T-cell derivation. 

The T-cell receptor does not act alone in recognizing and mediating the fate of target cells. Cytotoxic T cells also express a protein termed CD8 on their surfaces that is crucial for the recognition of the class I MHC-peptide complex. The abbreviation CD stands for cluster of differentiation, referring to a cell-surface marker that is used to identify a lineage or stage of differentiation. Antibodies specific for particular CD proteins have been invaluable... 

Serum amyloids Coagulation factors Tumor necrosis factor Erythrocyte proteins Apollpoprotelns Complement factors CD proteins... 

A. Overview The innate immune system initiates the defense against pathogens and antigenic insult. It involves the concerted actions of complement components, lysozyme, macrophages, and neutrophils. If the innate response is inadequate, the adaptive immune response is mobilized. This culminates in the activation of T lymphocytes, the effectors of cell-mediated immunity and the production of antibodies, by activated B lymphocytes, the effectors of humoral immunity. The cell types involved in immune responses can be identified by specific cell surface components or clusters of differentiation (CDs). For example, T helper cells bear the CD4 protein complex, whereas cytotoxic T lymphocytes express the CDS protein complex. Clusters of differentiation also can be used to characterize other types of hematopoietic cells, including precursors of granulocytes, megakaryocytes, and erythrocytes (Chapter 33). 

Figure 15 Typical protein CD spectra for particular secondary structural motife used in CD protein structure fitting programs.

Because antibodies, in theory, can be generated in the laboratory against any target, monoclonal antibodies can be used as a probe for detection of any cellular molecule. Initial applications used monoclonal antibodies for detection of cell surfece proteins for identification of cell types or the maturation stage of cells during differentiation. Because these surface proteins exhibited clustering, they became known as cluster of differentiation (CD) proteins. Nearly two hundred cluster of differentiation proteins are now known. 

Table 1 Putative uptake pathways for and Cd -protein complexes in mammalian cells. For further details, refer to the text. ...

CDCA, the only known Cd protein, was first identified in the model diatom T. weissflogii. Homolog genes have so far been found exclusively in diatom species [40,93]. They have also been found in all environmental samples that have been tested, suggesting that the use of Cd in CDCA likely accounts, at least partially, for the nutrient-like behavior of Cd in the oceans. 

---