<prompt> Invasive amoebiasis can be best diagnosed by -ELISACountercurrent immunoelectrophoresisHaemagglutination testComplement fixation test  <response>: Option 1,3 Amoebic Lectin Antigen GalNAG lectin is the principle virulence factor, present on the surface of trophozoites of pathogenic E. histolytica. Its various pathogenic mechanisms are: Adhsion, Cytotoxicity and Complement resistance. Serological tests ELISA, IHA etc. become positive only in Invasive amoebiasis. ELISA: detects 170kDa of lectin Ag in stool with 95 sensitivity and specificity. It can also differenciate pathogenic E. histolytica from non pathogenic E. disper Negative for Lectin Ag. IHA: it uses crude Ag to detect Amoebic Abs IgG. IgG appears only in the later stage of intestinal amoebiasis. Option 2 Electrophoresis: it is used for Isoenzyme Zymodeme analysis. Option 4 Complement fixation test: it is not used in diagnosis of amoebiasis. 