Kinetics of activation marker expression after in vitro polyclonal stimulation of chicken peripheral T cells

A comprehensive analysis of T cell activation markers in chicken is lacking. Kinetics of T cell activation markers (CD25, CD28, CD5, MHC-II, CD44, and CD45) in response to in vitro stimulation of peripheral blood mononuclear cells with concanavalin A (Con A) were evaluated between two chicken lines selected for high and low levels of mannose-binding lectin in serum (L10H and L10L, respectively) by flow cytometry. L10H chickens showed a stronger response to Con A based on the frequency of T cell blasts in both the CD4⁺ and CD8⁺ compartment. The majority of the proliferating CD4⁺ and CD8⁺ T cells expressed CD25. Proliferating T cells were seen both in the CD4⁺  MHC-II^+/- and CD8⁺  MHC-II^+/- population. For both CD4⁺ and CD8⁺ T cells, frequencies of CD25⁺ and MHC-II⁺ T cells were increased 24 h after stimulation. CD28⁺ frequencies were only increased on CD8⁺ T cells 48 h after stimulation. An increase in the relative surface expression based on mean fluorescence intensity (MFI) upon activation was observed for most markers except CD5. For CD4⁺ T cells, CD28 expression increased 24 h after stimulation whereas MHC-II expression increased after 48 h. For CD8⁺ T cells, a tendency toward an increase in CD25 expression was observed. CD28 expression started to increase 24 h after stimulation and only a transient peak in MHC-II expression on CD8⁺ T cells was observed after 24 h. CD44 and CD45 expressed on CD4⁺ and CD8⁺ T cells increased 24-72 h after stimulation. In summary, the frequency of CD25⁺ and MHC-II⁺ T cells were shown to be early markers (24 h) for in vitro activation of both CD4⁺ and CD8⁺ T cells. Frequency of CD28⁺ T cells was a later marker (48 h) and only for CD8⁺ T cells. Surface expression of all markers (MFI) increased permanently or transiently upon activation except for CD5.