A nonfunctional CD4 protein on a helper T cell would result in the helper T cell being unable to properly recognize and bind to antigens presented by antigen-presenting cells. This would impair the helper T cell's ability to activate other immune cells and coordinate an effective immune response.
Added by Joanne C.
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Step 1: A nonfunctional CD4 protein on a helper T cell would result in the helper T cell being unable to properly recognize and bind to antigens presented by antigen-presenting cells. Show more…
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If a B cell binds a protein antigen but does not get CD4 T-cell stimulation, what happens? T-cell help is not needed for protein antigens. It will generate only IgE antibody. It will not generate antibody but may later with T cell help. It will become permanently unresponsive.
Sri K.
In order to be activated, T cells require specific interaction with antigen presenting cells that display peptide antigens within MHC surface proteins. Indicate below, the correct association of CD8 or CD4 co-receptors with MHC class I or class II for helper T cells. You should also indicate the peptide antigen origins and brief description of the processing pathways. Be sure to mention the following for helper T cells: Co-receptor (CD4 or CD8) MHC (class I or class II) Origin of peptide antigen (exogenous or endogenous) Processing pathway description
Qudsiya A.
CD4 proteins on helper and regulatory T cells serve as co-receptors that bind to invariant parts of class II MHC proteins. CD4 is thought to increase the adhesion between T cells and antigen-presenting cells (APCs) that are initially connected only weakly by the T cell receptor bound to its specific peptide-MHC complex. To test this possibility, you label cell-surface MHC molecules with a fluorescently labeled peptide so that you can detect individual peptide-MHC complexes at the interface between the APCs and the T cells in a culture dish. To detect T cell responses-the sign of a productive contact-you load them with a $\mathrm{Ca}^{2+}$ indicator dye, as cytosolic $\mathrm{Ca}^{2+}$ increases when lymphocytes are active. You now count the peptideMHC complexes at a large number of interfaces (immunological synapses and measure the resulting uptake of $\mathrm{Ca}^{2+}$ in the adherent T cells (Figure $Q 24-4$, red circles). When you repeat the experiment in the presence of blocking antibodies against $\mathrm{CD} 4,$ you get a different result (blue circles). Do these results support or refute the notion that CD4 augments T cell receptor binding? Explain your answer.
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