Alterations induced by chronic stress in lymphocyte subsets of blood and primary and secondary immune organs of mice

Abstract

Background: The immune system is particularly sensitive to stress. Although acute stress generally has positive effects, chronic stress typically provokes immunosuppression. The elucidation of the mechanisms involved in immunosuppression are of interest for the design of therapeutic approaches to avoid the appearance of stress disorders. This study aimed to investigate chronic stress-induced alterations on lymphocyte subset distribution and percentages. The experiments were performed with C57BL/6 mice subjected to chronic immobilization stress.

Results: Stress caused a marked increase in apoptosis inside the thymus, and a reduction in the total number of thymocytes. Furthermore, the proportion of immature thymocytes declined significantly suggesting that the increased apoptosis mainly affected cells of immature phenotype. In blood, the total number of lymphocytes diminished but not all lymphocyte populations showed the same tendency: while the relative proportion of B cells declined slightly, the relative proportion of circulating CD3+ cells, and particularly some T cell subsets showing an immature phenotype (CD3+PNA+), increased under stress. The spleen and lymph nodes show a marked reduction in cellularity, but the relative proportion of T cells increased, while no change or only a slight reduction was observed in the relative proportion of B cells. Similarly, the relative proportion of T cells increased in bone marrow.

Conclusions: Detailed data on the alterations of lymphoid cell subsets occurring under immobilization stress, both in the bloodstream and in different lymphoid tissues, are obtained. In general, T cells are more affected than B cells and, in particular, a marked increase in the percentage of a subset of circulating PNA+CD3+ T cells is observed.

Figure 1

Effects of stress on thymic cell populations. A – Flow cytometry scatter plots for thymic cells from one control (top) and one stressed (bottom) mice. The plots show 5% of the total number of events, for one representative mouse from each group. Gates R1 (cell debris) and R2 (whole cells) were positioned by standard procedures. B – Histograms showing the number of annexin V⁺ (top) and PI⁺(bottom) cells in the corresponding R2 regions. C – Effects of stress on the percentage of events in regions R1 and R2. D – Effects of stress on the percentage of annexin V⁺ and PI⁺ cells in region R2. The experiment was done 3 times using 3 ≤ n ≤ 5 mice per group. Data for one representative experiment of the 3 are shown.

Figure 2

Effects of stress on the percentage of CD3⁺ and PNA⁺cells in region R2 (see Fig. 1). The experiment was done 4 times using 3≤ n ≤ 5 mice per group. Data for one representative experiment of the 4 are shown.

Figure 3

Effects of stress on peripheral blood cell populations. A – Effects of stress on the total number of white blood cells. B – Effects of stress on the percentage of PMN cells and lymphoid cells gated in the white blood cell region. The experiment was done 2 times using 3 ≤ n ≤ 5 mice per group. Data for one representative experiment of the 2 are shown.

Figure 4

Effects of stress on the percentages of lymphoid cell subsets in peripheral blood. A – Lymphoid, T and B cells. B – T cell subsets (CD3+, CD4+ and CD8+). C – PNA⁺ and PNA⁺CD3⁺ cells. The experiment was done 3 times using 3 ≤ n ≤ 5 mice per group. Data for one representative experiment of the 3 are shown.

Figure 6

Effects of stress on the percentages of T and B cell populations in the spleen, bone marrow and axillary lymph nodes. The experiment was done 3 times using 3 ≤ n ≤ 5 mice per group. Data for one representative experiment of the 3 are shown.

Figure 5

Dose-response in terms of proportions of CD4+ and CD8+ T cell subsets in the blood of stressed mice. The number of mice per group used in this experiment was n, 4 ≤ n ≤ 8.