Differential suppressive effects of testosterone on immune function in fresh water snake, Natrix piscator: an in vitro study

Abstract

Reptiles represent the crucial phylogenetic group as they were the ancestors of both birds and mammals hence very important to study. The objectives of the present study were to investigate the potential roles of testosterone in the innate immune responses and splenic lymphocyte proliferation in fresh water snake, Natrix piscator. Animals were mildly anesthetized and spleens were taken out to study the splenic macrophage phagocytosis, super oxide production and nitrite release using in vitro testosterone. Splenic lymphocytes were isolated by density gradient centrifugation and were studied for mitogen induced proliferation in presence of in vitro testosterone. Testosterone suppressed the phagocytosis and nitrite release in a concentration dependent manner. Biphasic suppressive effect of testosterone was observed in superoxide production as judged by reduction of nitroblue tetrazolium salt where salt reduction was suppressed at lower and higher concentrations of testosterone. Mitogen induced splenic lymphocyte proliferation was also suppressed by testosterone. By suppressing immune responses, testosterone may, therefore, act as a physiological mechanism regulating the relative amount of energy invested into either reproductive effort or immunocompetence.

Figure 1. Effect of different concentrations of testosterone on splenic macrophage phagocytosis in the fresh water snake, Natrix piscator.

The error bars bearing the same superscript do not differ significantly (Newman–Keul’s multiple-range test, p<0.05).

Figure 2. Effect of different concentrations of testosterone on NBT reduction in Natrix piscator.

The error bars bearing the same superscript do not differ significantly (Newman–Keul’s multiple-range test, p<0.05).

Figure 3. Effect of different concentrations of testosterone (T 10 to 1000– Testosterone 10 to 1000ng ml⁻¹) on nitrite release in Natrix piscator.

Effect of testosterone receptor antagonist cyproterone acetate (CPA, 100 ng ml⁻¹) is also shown. The error bars bearing the same superscript do not differ significantly (Newman–Keul’s multiple-range test, p<0.05).

Figure 4. Effect of in vitro testosterone on mitogen induced splenocyte proliferation in Natrix piscator.

Mitogens: ConA – Concanavalin A, 10 µg ml^–1; PHA – Phytohemagglutinin 10 µg ml^–1; LPS – Lipopolysaccharide, 20 µg ml^–1). The error bars bearing the same superscript do not differ significantly (Newman–Keul’s multiple-range test, p<0.05).