Lym 7.3: New Murine Specificity Defining Third Allele of the Ly 7 Locus

A new antigenic specificity, designated Lym 7.3, defines a third allele of the Ly 7 locus. The monoclonal antibody recognizing this determinant was produced by a hybridoma derived from immunization of B10.D2 Igⁿ mice against a (BALB/c x NZB) F₁ murine B lymphoma cell line (WEHI-5). Previously, we reported that another antibody (BD5-334.5) from this fusion reacted with an alloantigen similar or identical to the Ly 7.2 antigen originally described by McKenzie and coworkers. The Lym 7.3 specificity is qualitatively and quantitatively identical to the Lym 7.2 determinant in tissue distribution. Both antibodies react with a majority of splenocytes, peripheral blood lymphocytes, lymph node cells, and mitogen activated blasts from positive strains, but do not react with kidney, liver, or brain tissues by absorption analysis. B lymphocytes expressed significantly higher cell surface density of Lym 7.2 and Lym 7.3 than T lymphocytes. However, these antibodies clearly could be distinguished on the basis of inbred and congenic strain distribution. Three distinct phenotypes were presented: (1) Lym 7.2⁺ Lym 7.3⁺; (2) Lym 7.2⁺ Lym 7.3^-; and (3) Lym 7.2^- Lym 7.3^-. Genetic studies suggested both specificities were encoded by a single locus.