Lymphocyte adhesion to endothelium derived from human lymphoid tissue

Area of Science:

• Immunology
• Cell Biology
• Vascular Biology

Background:

• Efficient immune responses require lymphocytes to migrate to lymphoid organs.
• Lymphocyte extravasation involves binding to vascular endothelium.
• The role of adhesion receptors in lymphocyte migration to normal lymphoid organs is not fully understood.

Purpose of the Study:

• To isolate and characterize human tonsil-derived endothelial cells (TEC) for in vitro studies.
• To investigate the adhesion molecules involved in lymphocyte binding to TEC.
• To elucidate the specific mechanisms of lymphocyte extravasation into secondary lymphoid organs.

Main Methods:

• Isolation and culture of homogeneous endothelial cells from human tonsils.
• Flow cytometry (FACScan) for cell marker analysis (Von Willebrand factor, LVAP-2, FDC, IDC, macrophage markers).
• Adhesion studies using TEC, human umbilical cord endothelial cells (HUVEC), and various cell lines (Ramos, Daudi) with blocking antibodies (anti-VLA-4, anti-VCAM-1).

Main Results:

• Isolated TEC express endothelial markers (Von Willebrand factor, LVAP-2) and adhesion molecules (ICAM-1, VCAM-1, CD40), with inducible MHC class II.
• TEC bind lymphocytes via VLA-4 without cytokine pre-activation, unlike HUVEC.
• An anti-VLA-4 antibody blocked adhesion to TEC, while anti-VCAM-1 did not, indicating a VCAM-1-independent VLA-4 ligand on TEC.

Conclusions:

• Human tonsil-derived endothelial cells (TEC) provide a valuable in vitro model for studying lymphocyte homing.
• Lymphocyte adhesion to TEC involves VLA-4, utilizing a ligand distinct from VCAM-1 and fibronectin.
• This suggests a unique adhesion pathway facilitating lymphocyte entry into secondary lymphoid organs.