Age-related bias in function of natural killer T cells and granulocytes after stress: reciprocal association of steroid hormones and sympathetic nerves

Abstract

Stress-associated immune responses were compared between young (8 weeks of age) and old (56 weeks) mice. Since stress suppresses the conventional immune system (i.e. T and B cells) but inversely activates the primordial immune system (i.e. extrathymic T cells, NKT cells, and granulocytes), these parameters were analysed after restraint stress for 24 h. The thymus became atrophic as a function of age, and an age-related increase in the number of lymphocytes was seen in the liver. Although the number of lymphocytes in both the thymus and liver decreased as the result of stress, the magnitude was much more prominent in the thymus. To determine stress-resistant lymphocyte subsets, two-colour immunofluorescence tests were conducted in the liver and spleen. NKT cells were found to be such cells in the liver of young mice. On the other hand, an infiltration of granulocytes due to stress was more prominent in the liver of old mice than in young mice. Liver injury as a result of stress was prominent in young mice. This age-related bias in the function of NKT cells and granulocytes seemed to be associated with a difference in the responses of catecholamines (high in old mice) and corticosterone (high in young mice) after stress. Indeed, an injection of adrenaline mainly induced the infiltration of granulocytes while that of cortisol activated NKT cells. The present results suggest the existence of age-related bias in the function of NKT cells and granulocytes after stress and that such bias might be produced by different responses of sympathetic nerves and steroid hormones between young and old mice.

Fig. 1

Age-related and stress-associated changes in the number of MNC yielded by the thymus, liver and spleen. Young mice at the age of 8 weeks and old mice at the age of 56 weeks were used. Restraint stress was conducted for 24 h. The number of MNC was enumerated in 4 mice and the mean and one SD were produced.

Fig. 2

Estimation of stress-resistant lymphocyte subsets in the liver and spleen. (a) Two-colour staining of lymphocytes for various combinations. (b) Increase in the proportion of NKT cells in young mice and of granulocytes in old mice. MNC were obtained before and after stress in young and old mice and the phenotype of cells was identified by immunofluorescence tests. Numbers in the figure indicate the percentages of fluorescence-positive cells in corresponding areas. The mean and one SD in the proportion of NK cells, NKT cells and granulocytes were produced by repeated experiments (n = 4).

Fig. 3

NK-like cytotoxicity before and after stress in young and old mice. Lymphocytes were isolated from the liver and spleen, and NK-like cytotoxicity against YAC-1 cells was determined by 4 h-incubation at the indicated E/T ratios. The mean and one SD were produced in triplicate cultures.

Fig. 4

A comparison of the magnitude of liver injury between young and old mice after stress. To determine the magnitude of liver injury, serum levels of AST and ALT were measured. The mean and one SD were produced from 4 mice.

Fig. 5

Comparisons of serum levels of catecholamines and corticosterone between young and old mice after stress. Sera were obtained from 4 mice at each column to produce the mean and one SD.

Fig. 6

In vivo injection of adult mice (12 weeks of age) with (a) adrenaline (Adr) or (b) hydrocrotisone (Cor). MNC were isolated from the liver, spleen and thymus before and after each injection (24 h). Two-colour stainings for the indicated combinations were conducted. Representative results of three experiments are depicted.

Fig. 7

Hypothesis on two axes which connect stress with tissue injury, including (1) the adrenocortical axis with the activation of NKT cells and (2) the sympathetic nerve axis with the activation of granulocytes.