As we’ve seen over these past few months, a SARS-CoV-2 infection can result in widely different manifestations and severities in the subsequent course of the disease it causes, COVID-19. Many of those infected by SARS-CoV-2 experience a mild to severe illness, with symptoms that include fever, shortness of breath, cough, and fatigue that appear roughly 2-14 days after exposure to the virus. On the other hand, some individuals infected with the virus will remain asymptomatic.
A healthy immune system requires a series of checkpoints to ensure self tolerance and prevent damage to other tissues during immune response. Binding of costimulatory signal transduction molecules (such as CD28, ICOS, GITR) on T cells to their receptors (such as CD80/CD86, ICOSL, GITRL) on antigen presenting cells (APCs) may contribute to T cell activation. However, in some states, inhibitory signals of T cell activation and response occur during the involvement of T cell receptors. These signals are generated by proteins involved in immune checkpoints (eg, PD-1, CTLA-4, TIM-3, and LAG3). Usually PD-1 and CTLA-4 immunological checkpoint proteins are upregulated in T cells infiltrating tumors and bind to their respective ligands, PD-L1 (ligand B7-H1)/PD-L2 (ligand B7- DC) and CD80/86, and down-regulate T cell responses. Immunological checkpoint ligands are often upregulated in cancer cells as a means of evading immune detection. Therefore, immunotherapy by blocking immunological checkpoint protein activation of anti-tumor immunity has become a popular research subject for cancer therapy.
CD molecules are cell surface markers that appear or disappear when cells (leukocytes, red blood cells, platelets, and vascular endothelial cells, etc.) differentiate or become different lineages, different segments of cells, become active or diseased. Most CD molecules are transmembrane proteins or glycoproteins, including extracellular regions, transmembrane regions, and cytoplasmic regions. Some CD molecules are "anchored" on the cell membrane by means of inositol phospholipids. A few CD molecules are carbohydrate haptens. The study of CD molecules can be used in many basic immunology research fields, such as the relationship between CD antigen structure and function, cell activation pathway, signal transduction and cell differentiation, etc. It can be used clinically for disease mechanism research, clinical diagnosis, disease prognosis, efficacy tracking and treatment, and more.