Cell-mediated immunity of CD4 cells

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Cell-mediated immunity of CD4 cells


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Cell-mediated immunity of CD4 cells

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A 47-year-old man presents to a rural clinic for evaluation of fevers and abdominal pain, which have been ongoing for the past month. Laboratory testing demonstrates an elevated eosinophil count and elevated IgE level. ELISA testing confirms the presence of Toxocara cana antigens. Which of the following is released by the type of T-cell involved in mediating these laboratory changes and helping the body fight this infection?  

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First Aid








CD4+ T cells (HIV) p. 173

Helper T cells

cell surface proteins p. 108

cytokine secretion p. 106

in granulomatous diseases p. NaN

T cells p. 411

helper p. 98

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The key cells of the adaptive immune response are the lymphocytes - the B and T cells.

And there are two types of T cells.

T helper cells which express CD4 on their surface, and cytotoxic T cells which express CD8 on their surface.

Helper T cells primarily support other immune cells, whereas cytotoxic T cells kill cells that are infected with a pathogen or are cancerous.

Cell mediated immunity refers to the part of the immune response that’s based on cellular interactions, and cannot be transferred through serum from one person to another.

That makes sense since CD4 helper T cells interact with other immune cells to stimulate them.

Now, when a T cell is initially formed it’s considered naive.

This naive T cell is a bit like a student in school that isn’t ready to choose a career path.

Later when that T cell encounters an antigen - it gets activated or primed - and turns into an effector T cell.

This process of priming requires two signals.

The first signal is the antigen itself, which is usually presented on an MHC molecule on the surface of an antigen presenting cell like a macrophage or dendritic cell.

This antigen has to bind perfectly to the T cell receptor.

The second signal is called costimulation - and it’s when a ligand called CD28 on the surface of a T cell binds to a ligand called B7 on the antigen presenting cell.

This region, which includes the T cell receptor which binds to the MHC-Antigen, and CD4 and CD28 which bind with B7, is called the immune synapse.

Once the T cell receives both of these signals, a number of changes occur within the cell that transforms the naive T cell into an activated T cell.


CD4 cells are white blood cells that play a vital role in the body's cell-mediated immunity. Cell-mediated immunity is the part of the immune system which relies on phagocytes, cytotoxic T-lymphocytes, and the release of various cytokines to fight off an infection. CD4 cells recognize and destroy infected cells by binding to special proteins on the surface of the infected cells called antigens. Once attached, the CD4 cells release molecules called cytokines which activate other immune cells to destroy the infected cell.


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