Cytotoxic capabilities of bovine lymphocytes after lectin stimulation

Characterization and activation requirements of bovine lymphocytes acquiring cytotoxic activity after interleukin-2 treatment

Interleukin-2 (IL-2) treatment of cells and generation of non-major histocompatibility complex (MHC)-restricted cytotoxic cells from peripheral blood mononuclear leukocytes (PBML) was studied. Effector-target conjugate assays demonstrated that bovine PBML bound but did not lyse K562, HL60S and HL60R cells unless activated with IL-2. The magnitude of IL-2-activated killing of tumor cells as well as the magnitude of antibody-dependent cellular cytotoxicity depended on the IL-2 concentration. A short treatment (12-18 h) of effector cells with IL-2 was sufficient for development of cytotoxic activity. Withdrawal of IL-2 from the culture resulted in a reduction of cytotoxic activity that could be restored by further addition of IL-2. Cytotoxic activity of IL-2-activated populations obtained after nylon wool or Sephadex G-10 passage, and Percoll gradient centrifugation of PBML suggests that lymphokine-activated killer (LAK) cell activity in PBML is mainly mediated by a non-adherent lymphocyte lacking markers for B-cells. Positive and negative selection experiments using cell sorting confirmed these findings and demonstrated that the cell responsible for LAK cell activity in cattle belongs to a non-monocyte, non-B, CD2+ lymphocyte population. Furthermore, cytotoxic activity could not be generated in CD2+ populations enriched for cells expressing molecules equivalent to human and murine CD4 and CD8. These findings suggest that effector cells mediating non MHC-restricted cytotoxicity in cattle prevail in a population bearing a CD2+, CD4-, CD8- phenotype and that this population depends on the continuous presence of IL-2 for optimal cytotoxic function.

The role of bovine intraepithelial leukocyte-mediated cytotoxicity in enteric antiviral defense

The defense of a mucosal surface against viral infection is dependent in part on the leukocyte population resident at that site. In this study, leukocytes from the bovine intestinal epithelium were isolated and assessed for their ability to inhibit in vitro replication of an enteric pathogen, bovine coronavirus (BCV). As well, the intraepithelial leukocytes (IEL) were tested for their ability to mediate different types of cytotoxicity. The IEL were able to inhibit virus replication, and this activity was markedly enhanced by interleukin-2 and tumor necrosis factor. This combination of cytokines has similar effects on IEL-mediated cytotoxicity, which implicated cytotoxicity as a mechanism by which viral replication was limited. The IEL demonstrated enhanced cytotoxic function when compared with lymphocytes isolated from other sites in the gut-associated or systemic immune system. The IEL mediated higher levels of IL-2-activated, antibody-dependent, and lectin-dependent cytotoxicity than did lymphocytes from mesenteric lymph nodes, Peyer's patches, or the spleen. This function may be a reflection of the type of cell recruited to the epithelium, as indicated by the increased prevalence of T cells, and particularly CD8+ cells in the IEL population. Cytokine activation and the presence of a recognition signal, such as antibody, resulted in a synergistic increase in the level of IEL-mediated cytotoxicity. This type of interaction could serve to enhance the efficiency of IEL cytotoxic cells in vivo. Thus IEL-mediated cytotoxicity has the potential to serve as a mechanism of defense to enteric viral infection.

Effect of chronic administration of recombinant bovine tumor necrosis factor to cattle

Cachectin/tumor necrosis factor-alpha (TNF), a protein produced by macrophages upon stimulation, has been implicated as an important mediator of inflammatory processes and of clinical manifestations in chronic infectious diseases. In order to study further the potential role of TNF in infectious diseases, a homologous system was employed in which recombinant Escherichia coli (E. coli) derived bovine TNF (rBoTNF) was injected in cattle, either as a single bolus or in a repetitive treatment-regime. No clinical signs were observed, although changes occurred in hematologic and immunologic parameters when less than 0.5 mg of TNF/100 kg body weight was administered twice daily for 18 days. Prolonged treatment with 0.05-0.5 mg/100 kg induced histologic but no gross changes in the kidneys and liver. When doses were increased above 0.5 mg/100 kg, depression, anorexia, cachexia, and diarrhea appeared rapidly. Pathologic changes were apparent in various tissues including liver, kidneys, and lymphoid organs; body fat depots were depleted. Most of these changes appeared to be reversible; return to normal tissue-morphology occurred within 3 weeks of withdrawal of rBoTNF. The clinical and pathologic changes induced by prolonged rBoTNF administration resembled those observed in some chronic parasitic and viral infections of cattle in which macrophage-activation characteristically occur. Our finding may be relevant to the elucidation of the pathogenesis of these and other chronic infections.