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Role of human alveolar macrophages as antigen-presenting cells in Cryptococcus neoformans infection
A Vecchiarelli1, M Dottorini, D Pietrella
1Department of Experimental Medicine and Biochemical Sciences, University of Perugia, Italy.
Abstract:
The contribution of human alveolar macrophages (AM) from normal subjects in Cryptococcus neoformans infection was investigated. AM were able to efficiently phagocytize the fungus after opsonization, but killing activity did not occur at an effector-to-target ratio of 10:1 in a 6-h incubation since there was an inhibition of phagosome-lysosome fusion. Moreover, the role of AM as antigen-presenting cells was investigated. Cryptococcus-laden AM were co-cultured with autologous T lymphocytes and lymphoproliferation was determined; a massive blastogenic response of alpha/beta TCR-bearing T lymphocytes was observed. The response started after 1 day of co-culture and was triggered and regulated by IL-1 produced by AM in response to C. neoformans. Finally, the antigen-presentation process was associated with HLA class II DR molecules. This finding suggests that AM play a key role in the lung as antigen-presenting cells and, through the secretion of IL-1, regulate proliferation and activation of T lymphocytes, which are important in mediating pulmonary clearance. We speculate that in immunodepressive conditions, the impairment of AM functions could contribute to the spread of C. neoformans infection from the lung.
Insights
Human alveolar macrophages (AM) engulf Cryptococcus neoformans but struggle to kill it due to inhibited fusion. AM also activate T cells via IL-1 and HLA class II, crucial for lung immunity.
Area of Science:
- Immunology
- Cell Biology
- Pulmonary Medicine
Background:
- Alveolar macrophages (AM) are key immune cells in the lung.
- Cryptococcus neoformans is an opportunistic fungal pathogen.
- Understanding AM's role in C. neoformans infection is crucial for treating pulmonary disease.
Purpose of the Study:
- To investigate the function of human AM in Cryptococcus neoformans infection.
- To determine AM's capacity for phagocytosis, killing, and antigen presentation.
- To elucidate the mechanisms regulating T cell responses by AM.
Main Methods:
- In vitro phagocytosis and killing assays using opsonized C. neoformans and human AM.
- Co-culture of C. neoformans-laden AM with autologous T lymphocytes.
- Analysis of T lymphocyte proliferation and cytokine production (IL-1).
- Assessment of HLA class II DR molecule involvement in antigen presentation.
Main Results:
- AM efficiently phagocytosed opsonized C. neoformans.
- Killing activity was limited due to inhibited phagosome-lysosome fusion.
- AM effectively presented C. neoformans antigens, inducing massive T lymphocyte proliferation.
- IL-1 produced by AM regulated T cell activation, involving HLA class II DR.
Conclusions:
- Human AM play a critical role in initiating adaptive immune responses against C. neoformans in the lung.
- AM function as antigen-presenting cells, secreting IL-1 to drive T lymphocyte proliferation and activation.
- Impaired AM function in immunosuppression may contribute to C. neoformans dissemination.