Lymphocyte subpopulations in sheep during the early stage of experimental infection with bovine leukaemia virus

Abstract

Summary Stieep were experiraentalty infected with bovine leukaemia virus (BLV) by the inoculation of PBL from leukaemic sheep. Antibodies to viral structural proteins were detected at from 2 to 6 weeks after inoculation. At seroconversion, all sheep had a marked increase in the number of circulating lymphocytes, due essentially to an increase in the number of B cells. The number of circulating B cells then decreased but remained higher than pre-infection levels. A second increase in this population preceded the development of a B cell lymphoblastic leukaemia. Generalized lymphosarcoma was diagnosed at necropsy of all sheep. Variation between individual sheep in the time from infection to the development of tumours allowed two clearly delineated groups of nine sheep to be compared. A study of changes in the B cell and T cell populations during the first 16 weeks of infection suggested that the initial response to infection influences the subsequent rate of leukaemogenesis. At seroconversion the number of circulating B cells was significantly higher in group 1 (1016±l-51X10'/l)than in group2(6-47±276X10'/l). Group 1 sheep became leukaemic at 20-50 weeks after infection, whereas group 2 sheep did not do so until 70-95 weeks after infection.

Reduced proviral loads during primo-infection of sheep by Bovine Leukemia virus attenuated mutants

“…Together, these data demonstrate that primo-infection in sheep experimentally infected either with a wild type or mutant BLV proviruses is associated with a transient lymphocytosis, extending previous reports [11,12]. At seroconversion, all sheep exhibited a marked increase in the numbers of circulating B lymphocytes expressing for most of them the CD5 and CD11b cluster of differentiation markers and, interestingly, this phenomenon occurred independently of the type of mutant.…”

Dissemination of Bovine Leukemia Virus-Infected Cells from a Newly Infected Sheep Lymph Node

“…Blood-borne IgM ϩ cells, specifically IgM ϩ CD5 ϩ B cells (10), increase early during BLV infection of sheep and calves (11,29,50). The proliferation of IgM ϩ cells exceeds that for mock-infected controls and contributes to the increasing numbers of blood-borne B cells present at the time of seroconversion.…”

Lymphocyte subpopulations in sheep with lymphosarcoma resulting from experimental infection with bovine leukaemia virus

“…Suspensions of PBL in PBS containing 1% bovine serum albumin and 0-02% sodium azide (PBSA) were prepared by density gradient centrifugation from blood collected into EDTA, as described previously (11). A similar procedure was used to obtain lymphocyte suspensions from cell suspensions of lymph nodes, tumours and spleen, prepared by gently teasing the tissue samples in PBS and then filtering through gauze.…”

“…After washing twice with PBSA the cells were resus-pended in 50 /iL of a predetermined optimal dilution of fluoroscein isothiocyanate (FITC)-conjugated-rabbit anti-mouse immunoglobulins (Dakopatts) and incubated at 4°C for 45 min. After washing twice with PBSA, the cells as resuspended in 30 /iL PBS containing 01% sodium azide and semi-permanent slides for epifluorescence microscopy were prepared, as described previously (11). In each preparation the percentage of labelled cells was determined by counting at least 200 lymphocytes.…”

“…When infected sheep develop lymphocytosis, lymphoblastic leukaemia and generalized lymphosarcoma almost invariably follow (10). Nevertheless, there is considerable variation between individual sheep in the time from infection to the development of tumours (9,11).…”