T-lymphocyte subset distribution in human spleen

When analyzing human cellular immune responses, most focus is placed on the peripheral blood (PB) and, to a lesser extent, the lymph nodes. To date the spleen has not been analyzed with regard to its role in adaptive cellular immunity and more notably not with respect to T-cell immune responses.

We analyzed the splenic lymphocyte compartment in comparison with the PB lymphocyte compartment regarding the number of NK cells, B cells, CD4(+), CD8(+) T cells and CMV-specific CD8(+) T cells. Furthermore, we analyzed the distribution of naive, memory and effector subsets of CD4(+) and CD8(+) T cells in these compartments.

The spleen contains proportionally more B cells and less CD4(+) and CD8(+) T cells than PB. The percentage of CD8(+) T cells is greater in the spleen, leading to an inverse CD4/CD8 ratio. Both splenic CD4(+) and CD8(+) T-cell populations show a greater number of activated cells, and splenic CD8(+) T cells show a more differentiated cytotoxic CD27(-)CD45RA(+) memory phenotype.

Our findings show that the distribution of the different lymphocyte subsets is markedly different between the spleen and the PB, thus inferring an important and distinct role for the spleen in CD4(+) and CD8(+) T-cell activation.