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Although the cDNA of human decay accelerating factor (DAF) which restricts complement activation on homologous cell membranes was cloned in 1987, all trials to detect the cDNA of mouse DAF by cross-hybridization were unsuccessful. However, by immunoscreening with a rabbit antiserum against purified mouse DAF, we successfully cloned the cDNA. It contains four typical short consensus repeats (SCR) similar to that In human and guinea pig DAF. The base sequence showed 63.7 and 63.8% identIty to that of human and guinea pig DAF respectively. The deduced amino acid sequence identity to human and guinea pig DAF was 47.2 and 46.5% respectively. Mouse complement receptor related gene Y (Crry)/p65 function is comparable to DAF. SCR3 and SCR4 of mouse DAF showed 50% identity to SCR2 and SCR3 of Crty/p65 respectively. IdentificatIon of the mouse DAF gene should open a new approach for determining the actual in vlvo role of DAF by analyzing autoimmune mice as well as generating DAF gene knockout mice using embryonic stem cells. [ABSTRACT FROM AUTHOR]

Mannose-binding protein (MBP) plays an important role in host defense by recognizing sugar residues on certain pathogens and activating the complement cascade. Recently, we described a new protease, designated MBP-assoclated serine protease (MASP) which is required for complement activation by MBP. We have cloned the cDNA that encodes this protease and found that the deduced amino acid sequence contains an epidermal growth factor-like domain, two short consensus repeats and a serine protease domain. The overall structure of MASP is similar to serine proteases of the first complement component complex, C1r–C1s. Unlike C1r–C1s, however, MASP has a hlstidlne loop structure common to many serine proteases such as trypsin and chymotrypsin. The MASP gene was mapped on the long arm of chromosome 3 which is different from C1r–C1s as well as from trypsin and chymotrypsin. These findings suggest that MASP may have emerged prior to C1r–C1s from a common ancestor. This implies that MBP–MASP, a complex of lectin and serine protease, presumably evolved prior to adaptive immune recognition involving antibody and the classical complement pathway. [ABSTRACT FROM PUBLISHER]

Murine complement receptor type 2 (MCR2) is homologous to human CR2, whereas murine CR1 (MCR1) is structurally and evolutionary different from human CR1. Since ligand specificities of MCR1 and MCR2 are not completely clarified, we analyzed their functional characteristics to correlate them with structural information obtained in molecular biological studies. MCR1 and MCR2 purified from spleen cells were incubated with thlol-Sepharose bearing murine C3b, IC3b, or C3d in the presence or absence of various anti-MCR1 or-MCR1/MCR2 mAbs. Bound and free MCR1 and MCR2 were quantitated by Western biotting or two-site immunoradiometric assay. MCR2 bound to C3d and IC3b similarly efficiently, and 5-fold less efficiently to C3b. These bindings were completely inhibited by MCR1/MCR2-crossreactive antibodies 7G6 and 4E3. MCR1 bound to C3b efficiently and this was partially inhibited by MCR1-monospecific antibody 8C12, but not by 7G6 and 4E3. Combinations of 8C12 and 7G6 or 4E3 completely inhibited MCR1 binding to C3b. Therefore, two binding sites, one unique to MCR1 and the other shared with MCR2, are involved in MCR1 binding to C3b. MCR1 bound also to C3d and this was completely inhibited by 7G6 and 4E3. The binding of this solubilized MCR1 to C3d was as efficient as that of MCR2 to C3d. It seems, therefore, that the site shared by MCR1 and MCR2 that is recognized by both 7G6 and 4E3 binds to C3d and less efficiently to C3b. These results clarify the ligand specificities of MCR1 and MCR2. [ABSTRACT FROM PUBLISHER]