The
immune system is a vital part of our defenses against pathogens, but it
can also attack host tissues, resulting in autoimmune disease. The
antigens that induce destructive immune reactions can now be identified
directly—without any prior knowledge of their possible structure.
Molecules
that activate immune responses, generically termed antigens, are
recognized by circulating immune cells. In the case of autoimmune
reactions, such responses may lead to the destruction of body tissues. A
new method that can identify the antigens that initiate such reactions
may help to prevent misdirected attacks in the future. Using genetic
engineering techniques, researchers at LMU and the Max Planck Institute
for Neurobiology have generated cells that emit green fluorescent light
when stimulated by the binding of a cognate antigen.
The immunological needle in a haystack
The
new method is based on the isolation of T cells present in samples of
affected tissues obtained from patients with autoimmune diseases. The
research team, led by Dr. Klaus Dornmair (Institute for Clinical
Neuroimmunology at LMU and the Department of Neuroimmunology at the MPI
for Neurobiology), first recovered the genetic blueprints for the
specific antigen-binding T-cell receptors (TCRs) produced by these
cells, and transferred them into a cultured cell line that grows well in
the laboratory.
This
line also contains a version of the gene for the Green Fluorescent
Protein (GFP) that is specifically expressed if a TCR is activated.
Finally, the cells are incubated with a collection of some 100 million
peptides—short amino acid sequences like those normally recognized by
TCRs. If even a single peptide represented in the library is recognized
by a specific TCR, the corresponding cell synthesizes GFP and can be
detected by its green fluorescence, allowing the bound antigen to be
identified. The method thus provides a relatively simple way of
identifying single autoimmune antigens from huge numbers of possible
suspects.
An
initial test carried out using cells specific for a known influenza
antigen confirmed the efficacy of the method. The researchers were able
unequivocally to select out and identify the correct antigen from all
the other peptides used in the test. The technique is so rapid and so
sensitive that several million antigens can be analyzed in a matter of
hours. This opens up a wide range of possible applications—ranging from
the analysis of the reactive antigens responsible for autoimmune
diseases like multiple sclerosis or psoriasis to the identification of
new tumor or viral antigens. Indeed, its practical potential is so
significant that the method is the subject of a patent application.
