4.6. Crithidia luciliae immunofluorescence test (CLIFT)

CLIFT is an assay that was first introduced in 1975 [111], and it is similar to the IFA assay described above except for the source of the used antigenic substrate. The assay employs Crithidia luciliae protozoal cells as the source of antigenic DNA substrate as they possess a giant mitochondrion called kinetoplast that contains a giant mass of mitochondrial DNA. The kinetoplast was considered as a good substrate for the detection of anti-DNA autoantibodies because it is unlikely to be associated with nuclear antigens and can thus serve as a source of naked double-stranded DNA [111]. The assay proceeds exactly as IFA where the Crithidia luciliae cells are fixed on a glass slide and a series of dilutions of the patient's serum is incubated with the cells and detection is mediated through the addition of fluorescently labeled anti-IgG antibodies. CLIFT has been described to be highly specific to SLE similar to the Farr assay [97]. However, DNA of Crithidia luciliae was described to have a bent conformation similar to nucleosomal DNA which can result in the recovery of only a subset of anti-DNA antibodies, and thus the assay was described to have a low sensitivity [27, 97].
