The objective of this study was to characterize serum immunoglobulins and lymphocytes subpopulations in the peripheral blood mononuclear cells (PBMCs) of Holstein calves in response to lipopolysaccharide (LPS) challenge from Escherichia coli. Fourteen calves received subcutaneous injections of E. coli LPS at 10 weeks of age, and six calves were injected with saline as a control. The concentrations of total serum IgG and the relative amount of LPS-specific IgG in calves challenged with LPS were significantly higher (p<0.05) compared to control animals and LPS challenge significantly increased (p<0.05) the percentage of CD5 + and CD21 + T cells in PBMCs. Meanwhile, LPS challenge significantly increased (p<0.05, p<0.01) the percentage of CD8 + and CD25 + T cells in peripheral blood mononuclear cells (PBMC) at 7 and 14 Day-post LPS challenge (DPLC), respectively. The composition of CD4 + CD25 + T cells and CD8 + CD25 + T cells from calves challenged with LPS was also higher (p<0.05 and p = 0.562, respectively) than those of control calves at 14 DPLC. In conclusion, LPS challenge not only induces production of IgG with expression of B-cell immune response related cell surface molecules, but also stimulates activation of T-lymphocytes in PBMC. Our results suggest that LPS challenge in calves is a good model to elucidate cellular immune response against Gram-negative bacterial infections.

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