In a study on dwarf dogs with a weak immune system, giving them growth hormone for a month helped them look healthier and made the thymus (an immune organ) bigger, but it didn’t change the levels of thymosin‑alpha‑1 in their blood or improve how their immune cells responded to tests. The dogs already had normal thymosin‑alpha‑1 levels before treatment.

Immunodeficient dwarfism in Weimaraner dogs was characterized by failure to grow, emaciation, growth hormone (GH) deficiency, decreased lymphocyte blastogenic responsiveness to mitogens, lack of thymus cortex, and recurrent infections usually resulting in death. Affected pups did not respond to conventional supportive therapy, but did respond to treatment with thymosin fraction 5. Response to therapy with bovine GH was monitored by clinical observation, histopathologic examination of thymic biopsy material, lymphocyte blastogenic responsiveness to nonspecific mitogens, and radioimmunoassay of thymosin alpha 1 concentration in the serum. Growth hormone therapy (0.1 mg/kg of body weight/dose, 14 doses) during a 1-month period in 2 immunodeficient dwarf pups resulted in clinical improvement and a marked increase in the thickness and cellularity of the cortex of the thymus. Immunodeficient dwarf pups were not deficient in serum thymosin alpha 1 before GH therapy. Growth hormone therapy was not associated with a consistent increase in serum thymosin alpha 1 concentration or lymphocyte blastogenic responsiveness to mitogens.