Failure to Induce Mucosal Disease in Cattle Persistently Infected with Bovine Viral Diarrhea Virus by Treatment with Adrenocorticotropic Hormone

Abstract

Recent research has shown that cattle that develop mucosal disease (MD) often, if not always, have been persistently infected with bovine viral diarrhea virus (BVDV) since birth. The purpose of the present study was to determine whether MD could be induced by immunosuppression of persistently BVDV-infected cattle. For that purpose, adrenocorticotropic hormone (ACTH) was injected intramuscularly, twice daily for 5 consecutive days in 4 persistently BVDV-infected cattle and in 3 control cattle. Before the ACTH treatment, the numbers of leukocytes, neutrophils and mononuclear cells (MNC) per litre of blood in BVDV-infected cattle were in the same range as in the controls. Similarly, the proportions of B cells, T cells, monocytes and Fcγ⁺ cells (cells with receptor for the Fc part of IgG) were the same in the 2 groups of animals. On the other hand, the proliferative response to mitogen stimulation of MNC obtained from the control animals was twice as high as the corresponding value of the persistently BVDV-infected cattle.

In all animals, ACTH treatment caused increased Cortisol concentrations, leukocytosis, neutrophilia and decreased mitogen-induced lymphocyte stimulation. However, the MNC count and the proportions of B cells, T cells, Fcγ⁺ cells and monocytes remained unaltered. In spite of the immunosuppression, indicated by the decrease in mitogen-induced lymphocyte stimulation. ACTH treatment did not provoke any clinical signs of MD in the persistently BVDV-infected cattle.

Sammanfattning

Senare års forskning har visat att nötkreatur som utvecklar mucosal disease (MD) ofta har varit kroniskt infekterade med bovint virusdiarré virus (BVDV) sedan födelsen. Syftet med denna studie var att undersöka om en immunsuppression av persistent BVDV infekterade djur kan framkalla MD. Av detta skäl injicerades 4 kroniskt infekterade djur och 3 kontroller med adrenocortiocotropt hormon (ACTH) 2 gånger dagligen i 5 dagar. Före ACTH behandlingen var antalet leukocyter, neutrofiler och mononukleära celler (MNC) per liter blod hos kroniskt BVDV infekterade djur på samma nivå som hos kontrolldjuren. Även proportionerna B celler, T celler, monocyter och Fcγ⁺ celler (celler med receptor för Fc delen av IgG) var lika i de båda grupperna. Däremot svarade lymfocyter från kroniskt BVDV infekterade djur sämre på mitogenstimulering än vad lymfocyter från kontrolldjuren gjorde.

Alla djur svarade på ACTH behandling med stegrade cortisol värden i plasma, leukocytos, neutrofili och en minskad mitogen inducerad lymfocytproliferation. Antalet MNC och proportionerna av B celler, T celler, Fcγ⁺ celler och mononcyter förblev oförändrade under ACTH behandling. Trots den observerade immunosuppressionen, indikerad av den minskade benägenheten av lymfocyterna att svara på mitogen stimulering, framkallade ACTH behandling inga symtom på MD hos kroniskt BVDV infekterade djur.