Monoclonal Antibodies

E l ec t ron microscopy f i r s t r evea led the presence of filamentous structures intermediate in diameter between microfilaments (5-6 nm) and microtubules (20-25 nm) in eukaryotic cells. These intermediate, or 10-nm, filaments have subsequently been shown to compr ise f ive s e p a r a t e classes, distinguishable on the basis of their sub-unit molecular weights) t i ssue distr ibution~ and an t igen ic c h a r a c t e r i s t i c s (Laza r ides ) 1980; Anderton) 1981). Immunological cross-reactivities between different classes of filaments have been noted (Yen e t a l . , 1976; Blose et al., 1977; Bennett et al., 1978a,b; FelIini et al~i 197g), but the poss ibl i ty of c r o s s c o n t a m i n a t i o n of the or iginal i r n m u n o g e n makes such resu l t s d i f f i c u l t to i n t e r p r e t . No such ob jec t ion could be made t o a s imi lar analys is using monoclonal an t ibod ies , however (Mils te in , 1980). To confirm and extend the obse rva t ions made on the an t igen ic re la t ionsh ips and m o l e c u l a r identities of the subunits of mammalian neurofilaments) we have raised monoclonal antibodies to rat-brain intermediate filaments. Hof fman and Lasek (.1975)) on the basis of i n v i v o labelling studies of axonal transport) first proposed that mammalian neurof i l a ments comprise three proteins) of molecular weights 210 000, 155 000) and 70 000. More recent biochemical and immunological studies are in accord with this view (Micko & Schlaepfer) 1978; Liem e t a l . , 197gI Anderton e t a l . , 1978). Discrepancies none the le s s remain in the r epo r t ed tissue distribution and cross-reactivities of the three neurof i lament proteins. Several groups have demonstrated varying degrees of an t igen ic homology, in which either all three polypeptides appear similar or the 210 000and 155 00=mol.-wt. species share d e t e r m i n ants , whilst the 70 000-mol.-wt. polypeptide may be different (Liem et al., 1978; Anderton et. al., 1980; Dahl, 1980; Yen &Fields, 19g l ) . S ta in ing of neurones with antisera to the 70 000-mol.-wt. protein (Liem e t . a l . , 1978; 3acobs e t . a l . , 1980) may be the resu l t of a c rossreac t ion with the larger polypeptides) since others have failed to obtain positive immunofluorescence with antibody to this p ro te in (Ander ton e t . a l . , 1980; Dahl) 1980). Furthermore, the presence of the 70 000-mol.-wt. component in non-neuronal tissue has