Equine class II MHC antigens: identification of two sets of epitopes using anti-human monoclonal antibodies.

This research investigates equine lymphocytes using monoclonal antibodies that recognize HLA-DR, DQ and DP antigens in an attempt to identify cell surface class II MHC antigens, making use of both mouse and rat antibodies in addition to employing two-color fluorescence flow cytometry.

Background and Purpose

• The study aims to detect class II MHC antigens on the surface of equine lymphocytes.
• These lymphocytes are examined using mouse and rat monoclonal antibodies (mAb) that are capable of recognizing HLA-DR, DQ, and DP antigens.

Methods

• Peripheral blood lymphocytes (PBL) from thoroughbred horses were tested using these monoclonal antibodies.
• Two-color fluorescence flow cytometry was employed in the procedure to facilitate the detection of the antigens.

Findings

• Seven of the mAb reacted with both types of lymphocytes (surface immunoglobulin-positive (sIg+) as well as surface immunoglobulin-negative (sIg-)).
• sIg+ cells were observed to stain more brightly than sIg- cells, and this fluorescence pattern remained the same across different donors with each mAb applied.
• Among the mAb, SFR1-MI.2 exhibited varied intensities of reaction, as it stained cells from 47 out of 53 horses in a diversified manner.
• The immunoprecipitation method applying SFR1-MI.2 mAb also indicated light and heavy chains comparable to HLA class II alpha and beta chains obtained after being analyzed through two-dimensional electrophoresis.

Special Observations

• Antibody N297 (DQ specific) that has been previously identified to react with an epitope present only on human B cells rather than mitogen-induced T cells, exclusively reacted with sIg+ cells in 42 out of the 53 horses tested.
• The absence of staining of sIg- cells in horses with N297 might suggest either a minimal or no expression of this determinant on these cells, or maybe a weak cross-reactivity of this antibody with equine antigens.