Structure of complement factor H carboxyl-terminus reveals molecular basis of atypical haemolytic uremic syndrome.

Factor H (FH) is the key regulator of the alternative pathway of complement. The carboxyl-terminal domains 19-20 of FH interact with the major opsonin C3b, glycosaminoglycans, and endothelial cells. Mutations within this area are associated with atypical haemolytic uremic syndrome (aHUS), a disease characterized by damage to endothelial cells, erythrocytes, and kidney glomeruli. The structure of recombinant FH19-20, solved at 1.8 A by X-ray crystallography, reveals that the short consensus repeat domain 20 contains, unusually, a short alpha-helix, and a patch of basic residues at its base. Most aHUS-associated mutations either destabilize the structure or cluster in a unique region on the surface of FH20. This region is close to, but distinct from, the primary heparin-binding patch of basic residues. By mutating five residues in this region, we show that it is involved, not in heparin, but in C3b binding. Therefore, the majority of the aHUS-associated mutations on the surface of FH19-20 interfere with the interaction between FH and C3b. This obviously leads to impaired control of complement attack on plasma-exposed cell surfaces in aHUS.

Bone-marrow-derived cells contribute to the recruitment of microglial cells in response to beta-amyloid deposition in APP/PS1 double transgenic Alzheimer mice.

The role of microglia recruited from bone marrow (BM) into the CNS during the progression of Alzheimer's disease (AD) is poorly understood. To investigate whether beta-amyloid (Abeta) associated microglia are derived from blood monocytes, we transplanted BM cells from enhanced green fluorescent protein expressing mice into young or old transgenic AD mice and determined the engraftment of BM-derived cells into the brain and their relative distribution near Abeta deposits. When young transgenic mice were transplanted before the onset of AD-like pathology and the brains analyzed 6.5 months later, the number of engrafted cells was significantly higher than in age-matched wild type mice. Moreover, the number of BM-derived cells associated with Abeta was significantly higher than in old transgenic mice transplanted after the establishment of AD-like pathology. Local inflammation caused by intrahippocampal lipopolysaccharide injection significantly increased the engraftment of BM-derived cells in old AD mice and decreased the hippocampal Abeta burden. These results suggest that infiltration of BM-derived monocytic cells into the brain contributes to the development of microglial reaction in AD.

Complement factor H as a marker for detection of bladder cancer.

BACKGROUND: The BTA TRAK and BTA stat tests for bladder cancer use monoclonal antibodies (mAbs) X13.2 and X52.1 to detect factor H (FH)-related material in urine. The exact ligands remain unknown. METHODS: Western blot analyses of purified FH, recombinant factor H-related protein 1 (FHR-1), and serum and urine samples were used to identify the ligands of X13.2 and X52.1. Recombinant FH constructs were used to identify the target sites of X13.2 and X52.1. To analyze whether natural ligands of FH could compete with its recognition by the capture mAb X52.1, we used surface plasmon resonance analysis. The role of the ligands of X52.1 in the BTA TRAK assay was tested with use of purified proteins and FH-depleted samples. RESULTS: X13.2 bound to domain 3 of FH and FH-like protein 1, whereas X52.1 bound to domain 18 of FH and to FHR-1. Using specific FH depletion from a bladder cancer patient's urine and purified FH, we demonstrated that FH is the ligand recognized by the BTA TRAK test. By contrast, FHR-1 in urine reduced the FH-dependent test signal. CONCLUSIONS: FH is a tumor marker for bladder cancer. To reveal the presence of bladder cancer, the BTA TRAK assay detects FH, whereas FHR-1 is able to partly inhibit this detection. This indicates a special mechanism for a diagnostic immunoassay based on the combined effect of simultaneous positive and negative signals in a single sample.