Journal of Undergraduate Research


CD5 co-receptor, T helper cell activation, bacterial infection


Life Sciences


Microbiology and Molecular Biology


Properly functioning helper T cells are crucial in a response to an infection. The adaptive immune response is orchestrated by T helper cells and their function is dependent upon interactions between the T cell receptor (TCR), peptide MHC (pMHC) and co-receptors. Upon TCR interaction with a foreign antigen, a calcium signaling cascade is initiated, which determines T cell activation, survival, proliferation and differentiation. CD5 is a T cell co-receptor that is a negative regulator of T cell activation. T cells with higher CD5 expression respond better to foreign antigen than those with lower CD5 expression. Cell-surface expression of CD5 is proportional to T cell receptor signaling capacity for self-peptide. Because of this, CD5 acts to fine-tune the T cell response. Treatment with CD5 monoclonal antibodies causes increased intracellular Ca2+ in T cells.1 In our study, we examined the role of CD5 expression and calcium signaling in the T cell response to foreign antigen. To shed further light on this, we evaluated two helper T cells from T cell receptor transgenic mice (LLO118 and LLO56) that differ in primary and secondary response to a peptide of Listeria monocytogenes.2 They are also known to differ in CD5 levels.2 We found that each T cell has unique calcium mobilization in response to in vitro stimulation and that CD5 expression levels in these cells changed over time following stimulation. To further evaluate the role of CD5, we measured calcium signaling in CD5 knockout LLO118 and LLO56 T cells at three time points (naïve, day 3, day 8) and found that CD5 plays a significant role in promoting the calcium signaling of naïve CD5-high LLO56 T cells. LLO56, LLO118, and CD5 knockout LLO56 and LLO118 mice were bred and housed in pathogen free conditions. All mice used were 5–12 weeks old. All use of lab animals was done with approval of ACUC at BYU. Splenocytes from each type of mice were isolated and stimulated at three time points (naïve, 3rd day, and 8th day). Calcium flow cytometry was done to analyze the alteration of intracellular calcium concentrations in the T cells. This method allowed for identification and analysis of cells within a population based on their light-scatter profile and selective responsiveness to specific stimuli. To identify the T helper population, cells were labeled with fluorochrome-conjugated antibodies specific to mouse antigens. In our case, we selected the T helper cell population. Flou-4, a labeled calcium indicator that exhibits an increase in fluorescence upon binding to Ca2+, was used to measure the difference in signal levels.

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