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Uptake of antigen by afferent lymph dendritic cells mediated by antibody
G D Harkiss1, J Hopkins, I McConnell
1Department of Veterinary Pathology, University of Edinburgh, Edinburgh, GB.
Insights
Sheep afferent lymph dendritic cells bind antigen/antibody complexes via Fc receptors, enhancing immune responses. This rapid uptake mechanism, involving approximately two-thirds of cells, is crucial for secondary antigen challenge.
Area of Science:
- Immunology
- Cell Biology
Background:
- Dendritic cells are key antigen-presenting cells in the immune system.
- Understanding dendritic cell antigen uptake mechanisms is vital for vaccine development and immunotherapy.
Purpose of the Study:
- To investigate the binding and uptake of soluble protein and peptide antigens by sheep afferent lymph dendritic cells.
- To determine the role of antibodies and complement in antigen binding by these cells.
- To characterize the phenotype of dendritic cells involved in antigen uptake.
Main Methods:
- Isolation of dendritic cells from sheep afferent lymph.
- In vitro and in vivo assays using fluorescein-labeled antigens.
- Flow cytometry and two-color flow cytometry analysis.
- Assessment of antigen uptake in the presence and absence of specific antibodies and complement.
Main Results:
- Dendritic cells showed weak direct antigen binding, but uptake was significantly enhanced by specific antibodies in vitro and in vivo.
- Approximately 60% of dendritic cells actively took up antigens rapidly (within 5 min in vitro, 20-40 min in vivo).
- Sheep IgG subclasses mediated uptake, while F(ab')2 fragments were ineffective, suggesting an Fc receptor-mediated mechanism.
- Complement components did not affect antigen binding.
- CD1+ cells constituted 43% of those taking up antigen/antibody complexes, indicating a link to Langerhans' cells or skin dendritic cells.
Conclusions:
- Sheep afferent lymph dendritic cells primarily bind antigen/antibody complexes via Fc receptors.
- This Fc receptor-mediated uptake mechanism is rapid and efficient.
- The findings suggest a significant role for Fc receptors in the enhanced immune function of these dendritic cells during secondary antigen challenges.
Abstract:
Dendritic cells isolated from sheep afferent lymph were examined for their ability to bind soluble protein and peptide antigens labeled with fluorescein both in in vitro assays and following intradermal injection of antigen in vivo. Analysis of dendritic cells by flow cytometry revealed weak direct binding of proteins and peptide antigens. However, the degree of uptake was greatly enhanced in the presence of specific antibody in vitro or if antigen was injected intradermally into antigen-primed sheep. About 60% of dendritic cells possessed the ability to take up antigen in both the in vitro and in vivo experiments. The uptake of antigen occurred very rapidly, reaching maximum values in terms of cell numbers and fluorescence intensity in less than 5 min in vitro and 20-40 min following in vivo challenge. Both sheep IgG subclasses could mediate this effect, but F(ab')2 fragments were ineffective. Procedures adopted to remove complement components from the in vitro test mixtures did not result in any reduction in the binding of antigen by dendritic cells. Two-color flow cytometry analysis of the dendritic cell population further showed that 43% of cells taking up the antigen/antibody complexes were CD1+, suggesting a relationship between these cells and Langerhans' cells or other dendritic cells in skin. The results, thus, indicate that approximately two thirds of sheep afferent lymph dendritic cells bind antigen/antibody complexes via an Fc receptor, a mechanism which could be important in the accentuated accessory function of these cells known to occur following secondary antigen challenge.
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