Effects of age and recombinant equine somatotropin (eST) administration on immune function in female horses.

The research investigates the impact of aging and the administration of somatotropin (a hormone) on the immune system of female horses. It reports that while aging does lead to declines in certain aspects of the immune system, these declines were not reversed by the administration of somatotropin.

Research Context

• The study was conducted in relation to the understanding that aging generally results in a decrease in the levels of somatotropin and IGF-I (an insuline-like growth factor), along with a decline in immune function.
• The researchers aimed to study the effects of age and whether administering somatotropin could in any way reverse these declines in the immune systems of horses.

Methodology

• The researchers studied sixteen female standard bred horses, half of which were young and the other half were old.
• Each of these horses were given a daily dose of 10 mg/d recombinant equine somatotropin (eST) or a vehicle buffer for 49 days.

Findings

• The scientists observed that plasma IGF-I concentrations were generally higher in horses treated with eST, no matter the age group.
• There were lower numbers of monocytes (a type of white blood cell) and granulocytes (another type of white blood cell) in horses treated with eST.
• They also found that the older horses treated with eST had lower lymphocyte numbers (another type of white blood cell).
• The researchers noticed a trend that the percentage of CD4+ lymphocytes (a marker often used to evaluate immune system health) was typically higher in older horses, whereas the percentage of CD8+ lymphocytes was higher in younger horses.
• In response to certain substances, lymphocyte proliferation was not lower in older horses.

Conclusions

• Older mares treated with eST showed a lower peak primary antibody response to keyhole limpet hemocyanin (a standard test antigen used in immunology), whereas younger mares showed a higher one.
• The study concluded that the various declines in immune function associated with aging were not reversed with the administration of eST.