Ans. is 'a' i.e., Antinuclear antibody Autoantibodies in systemic lupus erythematosus (SLE)AntibodyPrevalence %Antigen RecognizedClinical UtilityAntinuclear98Multiple nuclearBest screening test; repeated negative tests make SLE unlikelyantibodiesAnti-dsDNA70DNA (double-stranded)High titers are SLE-specific and in some patients correlate with disease activity, nephritis, vasculitisAnti-SmAOProtein complexed to 6 species of nuclear U1RNASpecific for SLE; no definite clinical correlations; most patients also have anti-RNP; more common in blacks and asians than whitesAnti-RNP Protein complexed to U1RNAgNot specific for SLE; high titers associated with syndromes that have overlap features of several rheumatic syndromes including SLE; more common in blacks than whitesAnti-Ro (SS-A)30Protein complexed to hYRNA, primarily 60 kDa and 52 kDaNot specific for SLE; associated with sicca syndrome, predisposes to subacute cutaneous lupus, and to neonatal lupus with congenital heart block; associated with decreased risk for nephritisAnti-La (SS-B)1047-kDa protein complexed to hY RNAUsually associated with anti-Ro; associated with decreased risk for nephritisAntihistone70Histones associated with DNA (in nucleosome, chromatin) Phospholipids, b2More fequent in drug-induced ilupus than in SLEAntiphosphoilpid50glcoprotein 1 cofactor, prothrombinThree tests available-ELISAs for cardiolipin and b2Gl, sensitive prothrombin time (DRWT); predisposes to clotting, fetal loss, thrombocytopeniaAntierythrocyte60Erythrocyte membraneSurface and alteredMeasured as direct coombs' test; a small proportion develops overt hemolysisAntiplatelet30cytopiasmic antigens on plateletsAssociated with thrombocytopenia but sensitivity and specificity are not good; this is not a useful clinical testAntineuronal (includes anti- glutamate receptor)Antiribosomal P60Neuronal and lymphocyte surface antigensIn some series a positive test is CSF correlates with active CNS lupus.20Protein in ribosomesIn some series a positive test in serum correlates with depression or psychosis due to CNS lupusAbbreviations: CNS, central nervous system, CSF, cerebrospinal fluid; DRWT, dilute Russell viper venom time; ELISA, enzyme linked immunosorbent assay.