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The immunogenicity of antigen bound to the plasma membrane of macrophages
Abstract:
Macrophages were cultured for several hours after a brief exposure to radio-iodinated keyhole limpet hemocyanin. Most of the hemocyanin taken up by the macrophages was rapidly catabolized and eliminated from the cell. A few molecules were retained on the plasma membrane of the cells for prolonged periods and were not subject to endocytosis and catabolism. These few molecules of hemocyanin bound to the plasma membrane were identified by observing the fixation of antibody fragments to macrophages at low temperature. The membrane-bound antigen, which could be removed by trypsin or EDTA, was of large molecular size, though heterogeneous. A great part of the immune responses of mice to hemocyanin bound to live macrophages could be abrogated by treatment of the macrophages in vitro with antibody or trypsin. Hence, most of the immunogenicity of hemocyanin bound to macrophages was attributed to the few molecules of antigen bound to the plasma membrane.
Insights
Macrophages retain a few keyhole limpet hemocyanin molecules on their surface, which are crucial for immune responses. These membrane-bound antigens, not endocytosed, drive immunogenicity, unlike rapidly catabolized hemocyanin.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Macrophages play a key role in immune responses by interacting with antigens.
- Keyhole limpet hemocyanin (KLH) is a commonly used model antigen in immunological studies.
Purpose of the Study:
- To investigate the fate of keyhole limpet hemocyanin (KLH) after uptake by macrophages.
- To identify the components of macrophages responsible for initiating immune responses to KLH.
Main Methods:
- Macrophages were exposed to radio-iodinated KLH and cultured.
- Hemocyanin localization and fate were studied using antibody fragment binding and enzymatic treatments (trypsin, EDTA).
- The immunogenicity of KLH-bound macrophages was assessed by abrogating immune responses in mice after in vitro macrophage treatment.
Main Results:
- Most internalized KLH was rapidly degraded and eliminated by macrophages.
- A small fraction of KLH molecules remained bound to the macrophage plasma membrane.
- This membrane-bound KLH was large, heterogeneous, removable by trypsin/EDTA, and crucial for initiating immune responses.
Conclusions:
- The immunogenicity of KLH presented by macrophages is primarily due to a few molecules bound to the plasma membrane.
- These membrane-bound antigens are distinct from the bulk of endocytosed and catabolized KLH.
- Understanding this mechanism is vital for developing targeted immunotherapies and vaccines.