Use of an IgG fragment prepared with particulate plasmin to study the C1 binding and activation

Fc effector of anti-Aβ antibody induces synapse loss and cognitive deficits in Alzheimer's disease-like mouse model

Passive immunotherapy is one of the most promising interventions for Alzheimer's disease (AD). However, almost all immune-modulating strategies fail in clinical trials with unclear causes although they attenuate neuropathology and cognitive deficits in AD animal models. Here, we showed that Aβ-targeting antibodies including their lgG1 and lgG4 subtypes induced microglial engulfment of neuronal synapses by activating CR3 or FcγRIIb via the complex of Aβ, antibody, and complement. Notably, anti-Aβ antibodies without Fc fragment, or with blockage of CR3 or FcγRIIb, did not exert these adverse effects. Consistently, Aβ-targeting antibodies, but not their Fab fragments, significantly induced acute microglial synapse removal and rapidly exacerbated cognitive deficits and neuroinflammation in APP/PS1 mice post-treatment, whereas the memory impairments in mice were gradually rescued thereafter. Since the recovery rate of synapses in humans is much lower than that in mice, our findings may clarify the variances in the preclinical and clinical studies assessing AD immunotherapies. Therefore, Aβ-targeting antibodies lack of Fc fragment, or with reduced Fc effector function, may not induce microglial synaptic pruning, providing a safer and more efficient therapeutic alternative for passive immunotherapy for AD.

Initiation of complement activation

The complement system is an excellent one to look at as an example of a triggered enzyme system. It is found to use almost all the strategies of enzyme cascades and for initiation which were discussed in the introduction. The classical pathway is a fine example of an active zymogen form of activation and the alternative pathway is the canonical example of a tickover. Both may also be activated by exogenous enzymes from other systems. The strategies of enzymes waiting for substrates, of substrates waiting for enzymes, and of both waiting for modifying proteins are all seen in various stages of the reaction. There is an association of a linear cascade with the positive feedback amplification loop. This degree of evolutionary adaptation is not only aesthetically pleasing but must be taken to mean that the system is of considerable biological importance and has been over a long evolutionary time span.

Rapid three-step purification procedure for isolation of the C1q component of human complement and its use in a solid-phase C1q binding assay

A new procedure for the isolation of the C1q subcomponent of complement from human sera has been devised. The 3-step protocol employs DEAE Sephadex A-50, hydroxyapatite and Sephacryl S-200 chromatographies and can be performed within 9 h. It yields immunoglobulin-free homogeneous C1q protein with about 80% recovery. The isolated C1q protein is biologically active and may be used for the detection of circulating immune complexes in sera by the solid-phase C1q binding assay.

The structure and enzymic activities of the C1r and C1s subcomponents of C1, the first component of human serum complement

The subcomponents C1r and C1s and their activated forms C-1r and C-1s were each found to have mol.wts. in dissociating solvents of about 83000. The amino acid compositions of each were similar, but there were significant differences in the monosaccharide analyses of subcomponents C1r and C1s, whether activated or not. Subcomponents C1r and C1s have only one polypeptide chain, but subcomponents C-1r and C-1s each contain two peptide chains of approx. mol.wts. 56000 ("a" chain) and 27000 ("b" chain). The amino acid analyses of the "a" chains from each activated subcomponent are similar, as are those of the "b" chains. The N-terminal amino acid sequence of 29 residues of the C-1s "a" chain was determined, but the C-1r "a" chain has blocked N-terminal amino acid. The 20 N-terminal residues of both "b" chains are similar, but not identical, and both show obvious homology with other serine proteinases. The difference in polysaccharide content of the subcomponents C-1r and C-1s is most marked in the 'b' chains. When tested on synthetic amino acid esters, subcomponent C-1r hydrolysed both lysine and tyrosine ester bonds, but subcomponent C-1r did not hydrolyse any amino acid esters tested nor any protein substrate except subcomponent C1s. The lysine esterase activity of subcomponent C1s provides a rapid and sensitive assay of the subcomponent.