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Kinetics of chlamydial antigen processing and presentation to T cells by paraformaldehyde-fixed murine bone
1Immunology Section, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, Hamilton, Montana 59840-2999.
Abstract:
Macrophages are potential candidates for antigen presentation to chlamydial-specific CD4+ T cells. We have studied the kinetics of chlamydial antigen processing and presentation by using paraformaldehyde-fixed bone marrow-derived macrophages (BMDM) and splenic T cells isolated from chlamydia-infected mice. BMDM were inoculated with different multiplicities of heat-killed chlamydial elementary bodies, and at different times postingestion, the macrophages were fixed with paraformaldehyde and used as antigen-presenting cells in T-cell proliferation assays. T-cell proliferative responses were shown to be dependent on the chlamydial inoculum size, with a multiplicity of 10 chlamydiae per macrophage producing optimum T-cell proliferation. Temporal experiments showed that peak T-cell proliferative responses occurred between 4 and 12 h postingestion of chlamydiae by BMDM. T cells proliferated strongly to antigen when presented by H-2-matched BMDM but not when presented by H-2-disparate BMDM, demonstrating that T-cell recognition of processed chlamydial antigen was major histocompatibility complex restricted. BMDM inoculated with 10 chlamydiae per cell and fixed at 8 h postinoculation were shown to be as stimulatory to T cells as conventional splenic antigen-presenting cells. Because large numbers of BMDM can be propagated in vitro, and experimental conditions that provide optimum presentation of processed chlamydial antigen to chlamydia-specific CD4+ T cells can be defined, BMDM may be a potentially useful source for the isolation of naturally processed parasite antigen from major histocompatibility complex class II molecules.
Insights
Bone marrow-derived macrophages (BMDM) efficiently present chlamydial antigens to CD4+ T cells. Optimal antigen presentation occurs 4-12 hours post-infection, demonstrating Major Histocompatibility Complex (MHC) restriction.
Area of Science:
- Immunology
- Cell Biology
- Microbiology
Background:
- Macrophages are key antigen-presenting cells (APCs) for initiating adaptive immune responses.
- Chlamydia infections elicit CD4+ T cell responses, crucial for host defense.
- Understanding chlamydial antigen processing and presentation by macrophages is vital for vaccine development.
Purpose of the Study:
- To investigate the kinetics of chlamydial antigen processing and presentation by bone marrow-derived macrophages (BMDM).
- To determine optimal conditions for antigen presentation by BMDM to chlamydia-specific CD4+ T cells.
- To evaluate BMDM as a potential source for isolating naturally processed parasite antigens.
Main Methods:
- Bone marrow-derived macrophages (BMDM) were infected with heat-killed chlamydial elementary bodies at varying multiplicities.
- Macrophages were fixed with paraformaldehyde at different time points post-infection.
- T-cell proliferation assays were performed using fixed BMDM as APCs and splenic T cells from infected mice.
- Major histocompatibility complex (MHC) restriction was assessed using H-2-matched and H-2-disparate BMDM.
Main Results:
- T-cell proliferation was dependent on chlamydial inoculum size, with optimal response at 10 chlamydiae per macrophage.
- Peak T-cell proliferative responses occurred between 4 and 12 hours post-infection.
- Antigen presentation by BMDM was MHC class II restricted, confirmed by differential responses with H-2-matched and H-2-disparate cells.
- Optimally stimulated BMDM were as effective as conventional splenic APCs.
Conclusions:
- BMDM are effective APCs for presenting chlamydial antigens to CD4+ T cells in an MHC-restricted manner.
- Defined experimental conditions allow for optimal chlamydial antigen presentation by BMDM.
- BMDM represent a valuable in vitro system for isolating naturally processed parasite antigens from MHC class II molecules.