Human dendritic cells. Enrichment and characterization from peripheral blood

Area of Science:

• Immunology
• Cell Biology

Background:

• Dendritic cells (DC) with unique properties exist in rodent lymphoid tissues.
• Their presence and function in human peripheral blood were previously uncharacterized.

Purpose of the Study:

• To identify and characterize dendritic cells (DC) in human peripheral blood.
• To determine the role of human DC in initiating immune responses.

Main Methods:

• Enrichment of DC from human peripheral blood mononuclear cells using a multi-step isolation procedure.
• Characterization of enriched DC using light and electron microscopy, surface marker analysis (HLA, HLA-DR, leukocyte-common antigens), and functional assays.
• Comparison of DC function with monocyte, B cell, and T cell fractions in mixed leukocyte reactions and T cell proliferation assays.

Main Results:

• DC constitute 0.1-0.5% of human peripheral blood mononuclear cells and can be enriched to 20-60% purity.
• Enriched human DC share cytologic and surface marker similarities with rodent DC but possess distinct features, including complement receptors.
• Human DC lack phagocytic capacity and do not differentiate into monocytes or B cells in culture.
• DC-enriched fractions demonstrated significantly higher activity (10-fold or more) in stimulating allogeneic and syngeneic mixed leukocyte reactions and supporting T cell proliferation compared to other cell fractions.

Conclusions:

• Dendritic cells (DC) circulate in human peripheral blood and are distinct from other leukocytes.
• Human DC are the principal cell type required for initiating key immune responses, including allogeneic mixed leukocyte reactions.