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Cellular interactions regulating the in vitro response of bovine lymphocytes to ovalbumin
1International Laboratory for Research on Animal Diseases (ILRAD), Nairobi, Kenya.
Insights
CD4+ T cells are crucial for bovine lymphocyte proliferation to ovalbumin (OA). Other T cell types and B cells modulate these responses, with macrophages and B cells restoring responses when MHC class II is absent.
Area of Science:
- Immunology
- Veterinary Immunology
- Cellular Immunology
Background:
- Understanding the cellular basis of adaptive immune responses in cattle is vital for vaccine development and disease control.
- Bovine lymphocyte proliferation assays are used to assess cellular immunity against specific antigens like ovalbumin (OA).
Purpose of the Study:
- To investigate the roles of various immune cell populations, including T cells (CD4+, CD8+, gamma/delta TCR+), B cells, and macrophages, in the in vitro proliferative response of bovine lymphocytes to OA.
- To determine the necessity of MHC class II-restricted T cells for OA-specific immune responses.
Main Methods:
- Peripheral blood leukocytes (PBL) from OA-primed cattle were used for in vitro assays.
- Specific cell populations were depleted or purified from PBL using monoclonal antibodies and Fluorescence Activated Cell Sorting (FACS).
- Proliferative responses were measured in the presence or absence of specific cell populations and with the addition of T cell growth factor (TCGF).
Main Results:
- OA-specific proliferative responses were dependent on the presence of CD4+ T cells, which actively proliferated in response to antigen.
- Bovine CD8+ T cells and gamma/delta TCR+ T cells exhibited a suppressive effect on lymphocyte proliferation.
- Depletion of MHC class II+ cells abolished proliferation, which could be restored by adding macrophages or LPS-activated B cells.
Conclusions:
- CD4+ T cells are essential for initiating and driving proliferative immune responses to ovalbumin in cattle.
- CD8+ T cells and gamma/delta TCR+ T cells play regulatory, likely suppressive, roles in this response.
- Macrophages and B cells can compensate for the lack of MHC class II-dependent cells, highlighting their supportive role in T cell-mediated immunity.
Abstract:
We examined the contribution of MHC class II-restricted T cells (CD4+), MHC class I-restricted T cells (CD8+), gamma/delta T cell receptor (TCR)+ T cells, B cells and macrophages to the development and control of in vitro proliferative responses of bovine lymphocytes to ovalbumin (OA). Cell populations for in vitro assay were obtained from peripheral blood (peripheral blood leukocytes, PBL) of OA-primed cattle. Specific cell populations were depleted or purified from PBL by staining with monoclonal antibodies (MAbs) against the appropriate differentiation antigens and sorting on a Fluorescence Activated Cell Sorter (FACS). OA-specific in vitro responses of in vivo primed PBL were dependent on the presence of CD4+ T cells. Their presence could not be replaced by the inclusion of T cell growth factor (TCGF) in the culture system, indicating that CD4+ T cells probably actively proliferate in response to antigenic stimulation. Bovine CD8+ T cells and gamma/delta TCR+ T cells appeared to exert a suppressive effect on proliferative responses. No proliferation was observed in PBL after the depletion of MHC class II+ cells. In this case, the response could be restored by the addition of macrophages or LPS-activated B cells to the MHC class II- population.