Figure 1.

Biological activity of SpeA mutants. A. Mutations of amino acid position leucine 42 of SpeA to arginine or alanine resulted in greatly diminished interactions with cell surface MHC class II molecules, measured by laser fluorescence-activated flow cytometry and FITC-labeled rabbit anti-SpeA antibody. B. Mutations of amino acid position leucine 42 of SpeA to arginine or alanine resulted in greatly diminished activation of human lymphocytes. Human T-cell proliferation was assessed by [³H]thymidine incorporation (12 h pulse) after 60 h of culture. Each data point represents the mean of triplicate determinations; SEM ≤ 5%.