Stroma-dependent development of two dendritic-like cell types with distinct antigen presenting capability

Area of Science:

• Immunology
• Cell Biology
• Hematopoiesis

Background:

• Antigen-presenting cells (APCs) are crucial for adaptive immunity.
• Dendritic cells (DCs) are key APCs with distinct subsets and functions.
• The spleen contains various immune cell populations, including DCs.

Purpose of the Study:

• To characterize novel APCs found in murine spleen cultures.
• To differentiate these novel cells from conventional dendritic cells (cDCs).
• To investigate the functional capabilities and origins of these distinct APC subsets.

Main Methods:

• Utilized long-term spleen cultures (LTC) and bone marrow progenitor co-cultures with splenic stromal line 5G3.
• Employed flow cytometry to identify cell surface markers (CD11c, CD11b, MHC-II, CD8α).
• Assessed antigen cross-presentation to CD8(+) and CD4(+) T cells.
• Analyzed cytokine gene expression using quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR).

Main Results:

• Identified a novel APC subset, L-DCs (CD11c(lo)CD11b(hi)MHC-II(-)CD8α(-)), characterized by high endocytic activity.
• L-DCs and cDC-like cells both cross-present antigens to CD8(+) T cells.
• L-DCs, lacking MHC-II, fail to activate CD4(+) T cells, unlike MHC-II(+) cDC-like cells.
• L-DCs are continuously produced in vitro, suggesting self-renewing progenitors, distinct from transient cDC-like cells.
• Significant differences in cytokine expression were observed between L-DCs and cDC-like cells.

Conclusions:

• Two distinct APC subsets, L-DCs and cDC-like cells, are produced in vitro from splenic stroma.
• L-DCs represent a novel population of dendritic-like cells with unique antigen-presenting capabilities.
• These subsets appear to originate from different lineages and are not developmentally linked.
• Splenic stroma plays a role in supporting the production of diverse APC populations.