High-molecular-weight Ly-5 isoforms expressed on T cells: activation-dependent expression

Area of Science:

• Immunology
• Molecular Biology

Background:

• Granular T lymphocyte (GTL) lines derived from murine spleen express Ly-5 antigen, typically found on B-lineage cells.
• This Ly-5 antigen on GTL lines exhibits a B220-epitope, recognized by 6B2 monoclonal antibodies (mAbs).

Purpose of the Study:

• To characterize the Ly-5 isoform expressed on GTL lines.
• To investigate the molecular basis and expression patterns of this unique Ly-5 isoform.

Main Methods:

• Immunoprecipitation analysis to determine molecular weight and epitope expression.
• Endoglycosidase treatment to assess core protein size.
• Sequential immunoprecipitation using 6B2 and 14.8 mAbs.
• Northern blot and polymerase chain reaction (PCR) analysis of Ly-5 transcripts.

Main Results:

• A high-molecular-weight Ly-5 isoform (260 kd) was identified on GTL lines, distinct from the B220 isoform (240 kd) on pre-B cells.
• Size differences were confirmed after endoglycosidase treatment, suggesting distinct core protein sizes.
• The GTL Ly-5 isoform predominantly expressed the '6B2 epitope', while B220 isoform expressed the '14.8 epitope'.
• Northern blot analysis did not reveal distinct mRNA for the 260 kd Ly-5, but PCR suggested transcription from a unique promoter.
• This 6B2+ Ly-5 isoform was rapidly induced on T cells upon interleukin-2 (IL-2) stimulation in vitro, functioning as an activation antigen.

Conclusions:

• Murine GTL lines express a unique, high-molecular-weight Ly-5 isoform with a B220-epitope.
• This Ly-5 isoform is distinct from the B220 isoform found on B cells, with differences in molecular weight and core protein size.
• Evidence suggests the 260 kd Ly-5 isoform is regulated by a distinct promoter and alternative exon(s).
• The 6B2+ Ly-5 isoform serves as an activation antigen on T cells, rapidly induced by IL-2 stimulation.