Cell-mediated cytotoxicity of peripheral blood mononuclear cells stimulated in vitro for infectious bovine rhinotracheitis virus-infected cells

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.

Determination of BHV1 specific immune reactivity in naturally infected and vaccinated animals by lymphocyte proliferation assays

The in vitro BHV1-specific lymphocyte stimulation assay was used to investigate immune reactivity of cattle after natural infection or vaccination with BHV1. Proliferative responses to live virus were shown in tests with peripheral blood lymphocytes of seropositive field virus-infected animals and of vaccinated animals. Nineteen out of 36 seropositive field virus-infected animals did not show in vitro responses. Nine out of 12 animals showed, at least transient, responsiveness after vaccination. Antibody titers were maintained throughout the observation period. T cell activity is believed to play a role in protection against BHV1 infection. The in vitro proliferative assay, however, can not discriminate between BHV1 seropositive and seronegative field virus-infected animals. After vaccination, the BHV1-specific lymphocyte responses of at least one animal disappeared. Both observations may point to the fact that T cell memory is generated, or at least systemically present, to a limited extent.

Bovine natural cell mediated cytotoxicity (NCMC): activation by cytokines

Incubation of bovine peripheral blood mononuclear leukocytes (PBML) with the cytokines (CK) IL-2, alpha-IFN, gamma-IFN or IL-4 resulted in significant increases in natural cell mediated cytotoxicity (NCMC) over endogenous levels, as determined in an 18 h 51Cr-release assay using the human K562 or mouse Yac-1 target cell lines. Endogenous cytotoxic activity of bovine natural effector cells (NEC) using K562 or Yac-1 target cells was minimal (killing less than 8%). After 18 h of incubation with the CK hurIL-2, alpha-bovrIFN, gamma-bovrIFN or hurIL-4, NEC had significant increases in cytotoxic activity for both K562 and Yac-1 target cells. Significant increases in cytotoxic activity were not found after incubation of NEC with IL-1 or beta-IFN. Specific killing varied with CK concentration in a dose dependent manner and was proportional to effector:target cell ratio. Activation of the bovine NEC by CK was rapid, occurring within 6-12 h of incubation with alpha-IFN or gamma-IFN and within 12-18 h of incubation with IL-2. Incubation of bovine PBML with IL-2 and alpha- or gamma-IFN or with alpha-IFN and gamma-IFN showed that these CK do not act in a synergistic manner to increase NCMC in the bovine NEC.

Cytotoxic capabilities of bovine lymphocytes after lectin stimulation

Bovine peripheral blood mononuclear leukocytes (PBML) were stimulated in vitro with the mitogenic lectins concanavalin A (Con A) and phytohemagglutinin. Their cytotoxic capabilities were evaluated in a 51Cr release assay. Lectin-activated bovine effector cells did not mediate antibody dependent cellular cytotoxicity (ADCC) nor direct killing against cultured tumor target cells. Nevertheless, activation of PBML with lectins consistently generated effector cells able to mediate lectin-dependent cellular cytotoxicity. Cultivation of Con A stimulated-PBML for 3 to 4 weeks in the presence of lymphokines-containing IL-2 generated cells with the ability to mediate lysis without using Con A-coated target cells. However, cytotoxic cultures capable of mediating direct lysis of target cells were not able to mediate ADCC.

Natural cell-mediated cytotoxicity to cells infected with infectious bovine rhinotracheitis virus

Cell-mediated cytotoxicity against viral-infected cells was demonstrated in a 6-hr 51Cr release assay. Peripheral blood mononuclear leukocytes from both infectious bovine rhinotracheitis virus (IBRV)-infected and noninfected cattle exhibited preferential lysis against IBRV-infected primary bovine embryonic kidney (BEK) cells compared to cells infected with pseudorabies virus and noninfected BEK cells. Addition of specific antibody to the assay did not enhance cytotoxicity. The effector cell was a nonadherent cell which was either spontaneously enriched or generated during in vitro cultivation. Maximal cytotoxic activity was detected in peripheral blood mononuclear cells cultured for 3 to 5 days. Several factors affected the magnitude of cytotoxicity during the assay: target cell type, concentration of viral inoculum, duration of effector and target cell contact. It is suggested that target cell lysis was a form of natural cell-mediated cytotoxicity mediated by a cell which has different characteristics from the typical human and murine NK cell.