The CD4 molecule is expressed not only in T lymphocytes, but also in NKT cells, B cells, monocytes, and granulocytes (+ other?).
Dear Maria-Luiza,
T lymphocytes are defined as CD3+TCR+ cells. T cells are 55-65% of all leukocytes in peripheral blood of healthy donors. The normal ratio of CD3+CD4+ : CD3+CD8+ is 2:1. Additionally, NKT, Treg, DC, and monocytes express CD4. Ratio of CD4+ monocytes in peripheral blood is very variable and depends on individual lifestyle (i.e. ratio in peripheral blood of smokers is significantly higher compared to non-smokers). Therefore, count of whole CD4 is not useful to analyze the peripheral blood of autoimmune patients, detailed analyzes of cell subsets and i.e. IL-17+ or IFN-g+ CD4+CD3+ T effector cells in combination with defined activation markers should be investigated.
There is an overproduction of proinflammatory cytokines produced from TH1 CD4+ cells. Additionally, some subpopulations of CD4+ T cells are "Cytotoxic cells". The latest can escape negative selection and interact with self antigens under certain conditions. The cytotoxicity of these cells occurs only by Fas / FasL or TNF / TNFRI interaction (not by perforin / granzyme-induced apoptosis).
Dear Maria-Luiza,
T lymphocytes are defined as CD3+TCR+ cells. T cells are 55-65% of all leukocytes in peripheral blood of healthy donors. The normal ratio of CD3+CD4+ : CD3+CD8+ is 2:1. Additionally, NKT, Treg, DC, and monocytes express CD4. Ratio of CD4+ monocytes in peripheral blood is very variable and depends on individual lifestyle (i.e. ratio in peripheral blood of smokers is significantly higher compared to non-smokers). Therefore, count of whole CD4 is not useful to analyze the peripheral blood of autoimmune patients, detailed analyzes of cell subsets and i.e. IL-17+ or IFN-g+ CD4+CD3+ T effector cells in combination with defined activation markers should be investigated.
Thank you, Helmut! May I add a question - what is the proportion of Th2 cells among the CD4+ T cells in peripheral blood of healthy individuals?
Dear Maria-Luiza,
Simple question but difficult answer:
The murine Th1/Th2 model cannot be simply transferred to the human system since, mice are not man!
Th2 cells defined as IL-4+ T cells are very rare in human blood. Most researchers (especially allergists) define human Th2 as IL-5+IL-13+INF-g- cells. However, these subset detectable in blood donors with active type I allergy is rather undetectable in healthy donors. The dominant Th cell population in healthy donors produces IFN-g after stimulation.
Indeed, the existence of Th1/Th2 cell subpopulations was initially proposed in mice based on the cytokines they produce. However, the amount of cytokines produced in humans by CD4+ T cells varies with populations, and "negative" concentrations can often be found. Also, the variations can be determined only statistically using percentiles by referring to values of healthy control subjects. Finally, Th1/Th2 subpopulations in humans can also be determined using chemokines (eg Th2: CCL17 / TARC, CCL22, Th1: CXCL9, CXCL10, etc.).
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