Figure 2

FACS analysis of peripheral blood lymphocytes (gated) of patient 1, pre-treatment (A) and during flare (B). Isotype (Becton Dickenson) is shaded, solid line shows T cell binding of efalizumab-FITC (custom design, Genetech), and dotted line shows binding of an anti-CD11a antibody which binds to a different epitope (clone 25.3, Immunotech). The pre-treatment sample (A) shows high-level binding of both anti-CD11a antibodies. The sample acquired during flare (B) shows the ex-vivo level of binding of efalizumab-FITC is the same as isotype, as there is already saturation of this CD11a epitope by therapeutic administration of efalizumab. There is also reduced binding of the 25.3 epitope indicating significant down-regulation of CD11a surface expression.