SLA and autoimmune hepatitis: When HEK293 expressing SLA, either fixed with acetone or 1% (w/v) formalin in acetone, were used as substrates in indirect immunofluorescence (IFA), all 20 anti-SLA positive AIH sera produced a cytoplasmic staining pattern (Figure 3(a)) that was absent in the wild-type HEK293 (Figure 3(b)).