Infiltrating T lymphocytes in the kidney increase oxidative stress and participate in the development of hypertension and renal disease

Abstract

The present studies examined the role and mechanism of action of infiltrating T lymphocytes in the kidney during salt-sensitive hypertension. Infiltrating T lymphocytes in the Dahl salt-sensitive (SS) kidney significantly increased from 7.2 ± 1.8 × 10(5) cells/2 kidneys to 18.2 ± 3.9 × 10(5) cells/2 kidneys (n = 6/group) when dietary NaCl was increased from 0.4 to 4.0%. Furthermore, the expression of immunoreactive p67(phox), gp91(phox), and p47(phox) subunits of NADPH oxidase was increased in T cells isolated from the kidneys of rats fed 4.0% NaCl. The urinary excretion of thiobarbituric acid-reactive substances (TBARS; an index of oxidative stress) also increased from 367 ± 49 to 688 ± 92 nmol/day (n = 8/group) when NaCl intake was increased in Dahl SS rats. Studies were then performed on rats treated with a daily injection of vehicle (5% dextrose) or tacrolimus (0.25 mg·kg(-1)·day(-1) ip), a calcineurin inhibitor that suppresses immune function, during the period of high-NaCl intake (n = 5/group). In contrast to the immune cell infiltration, increased NADPH oxidase expression, and elevated urine TBARS excretion in vehicle-treated Dahl SS fed high salt, these parameters were unaltered as NaCl intake was increased in Dahl SS rats administered tacrolimus. Moreover, tacrolimus treatment blunted high-salt mean arterial blood pressure and albumin excretion rate (152 ± 3 mmHg and 20 ± 9 mg/day, respectively) compared with values in dextrose-treated Dahl SS rats (171 ± 8 mmHg and 74 ± 28 mg/day). These experiments indicate that blockade of infiltrating immune cells is associated with decreased oxidative stress, an attenuation of hypertension, and a reduction of renal damage in Dahl SS rats fed high salt.

Fig. 1.

Thiobarbituric acid-reactive substances (TBARS) in urine (A) and in renal tissue (B) of Dahl salt-sensitive (SS) rats maintained on 0.4 or 4.0% NaCl diet for 3 wk. *P < 0.05 vs. 0.4% NaCl-fed animals.

Fig. 2.

A: total number of T lymphocytes isolated from both kidneys of Dahl SS rats maintained on 0.4 or 4.0% NaCl diet for 3 wk. Immunohistochemical localization of T cells in the renal cortex (B and C) and medulla (D and E) of Dahl SS rats fed 0.4% (B and D) or 4.0% NaCl chow (C and E). T cells were localized in the renal tissue with antibodies directed against the cell surface marker CD43 (original magnification ×20). *P < 0.05 vs. 0.4% NaCl-fed animals.

Fig. 3.

Influence of chronic treatment with the immunosuppressant agent tacrolimus on mean arterial blood pressure (A) and albumin excretion rate (B) in Dahl SS rats fed 4.0% NaCl for a period of 3 wk. *P < 0.05 vs. vehicle-treated animals.

Fig. 4.

Light microscopy images of trichrome-stained sections of renal outer medulla (×10 original magnification; A-B) and renal cortex (×40 original magnification; C–D) of Dahl SS rats receiving daily injections of vehicle (A and C) or tacrolimus (B and D) during the 3-wk period they were fed 4.0% NaCl diet. Bottom: calculated glomerular injury score (E) and the percentage of renal outer medulla (OM) consisting of protein casts (F). *P < 0.05 vs. vehicle-treated animals.

Fig. 5.

Effects of chronic treatment with the immunosuppressant tacrolimus during the high-salt period on the absolute numbers of infiltrating T lymphocytes (A) and on the expression of NADPH subunit p67^phox (B) in the renal tissue of Dahl SS rats. *P < 0.05 vs. vehicle-treated animals. †P < 0.05 vs. 0.4% NaCl-fed animals.

Fig. 6.

Expression of p67^phox in renal tissue and renal T lymphocytes obtained from Dahl SS rats fed 0.4 or 4.0% NaCl diet for 3 wk. *P < 0.05 vs. expression in tissue; 100 μg of protein or 2.5 × 10⁵ cells were loaded per well.

Fig. 7.

Calculated NADPH oxidase subunit expression, normalized to low-salt diet, contributed by infiltrating T lymphocytes in kidneys of rats fed 0.4 or 4.0% NaCl for 3 wk. *P < 0.05 vs. expression of same subunit in 0.4% NaCl-fed animals.

Fig. 8.

Effect of chronic administration of the antioxidant tempol on mean arterial blood pressure (A) and albumin excretion rate (B) in Dahl SS rats fed 4.0% NaCl for a period of 3 wk. *P < 0.05 vs. vehicle control animals.