Serum Complement Activation by C4BP-IgM Fusion Protein Can Restore Susceptibility to Antibiotics in Neisseria gonorrhoeae

Research Advances in Fusion Protein-Based Drugs for Diabetes Treatment

Diabetes mellitus (DM) is a chronic metabolic disease characterized by elevated blood glucose levels, resulting in multi-organ dysfunction and various complications. Fusion proteins can form multifunctional complexes by combining the target proteins with partner proteins. It has significant advantages in improving the performance of the target proteins, extending their biological half-life, and enhancing patient drug compliance. Fusion protein-based drugs have emerged as promising new drugs in diabetes therapeutics. However, there has not been a systematic review of fusion protein-based drugs for diabetes therapeutics. Hence, we conducted a comprehensive review of published literature on diabetic fusion protein-based drugs for diabetes, with a primary focus on immunoglobulin G (IgG) fragment crystallizable (Fc) region, albumin, and transferrin (TF). This review aims to provide a reference for the subsequent development and clinical application of fusion protein-based drugs in diabetes therapeutics.

Diverse Functions of C4b-Binding Protein in Health and Disease

C4b-binding protein (C4BP) is a fluid-phase complement inhibitor that prevents uncontrolled activation of the classical and lectin complement pathways. As a complement inhibitor, C4BP also promotes apoptotic cell death and is hijacked by microbes and tumors for complement evasion. Although initially characterized for its role in complement inhibition, there is an emerging recognition that C4BP functions in a complement-independent manner to promote cell survival, protect against autoimmune damage, and modulate the virulence of microbial pathogens. In this Brief Review, we summarize the structure and functions of human C4BP, with a special focus on activities that extend beyond the canonical role of C4BP in complement inhibition.

Clinical Isolates of Acinetobacter spp. Are Highly Serum Resistant Despite Efficient Recognition by the Complement System

Gram-negative bacteria from the genus Acinetobacter are responsible for life-threating hospital-related infections such as pneumonia, septicemia, and meningitis, especially in immunocompromised patients. Worryingly, Acinetobacter have become multi- and extensively drug resistant (MDR/XDR) over the last few decades. The complement system is the first line of defense against microbes, thus it is highly important to increase our understanding of evasion mechanisms used by Acinetobacter spp. Here, we studied clinical isolates of Acinetobacter spp. (n=50), aiming to characterize their recognition by the complement system. Most isolates tested survived 1 h incubation in 30% serum, and only 8 isolates had a lower survival rate, yet none of those isolates were fully killed. Intriguingly, four isolates survived in human whole blood containing all cell component. Their survival was, however, significantly reduced. Flow cytometry analyses revealed that most of the isolates were detected by human IgG and IgM. Interestingly, we could not detect any significant concentration of deposited C1q, despite observing C4b deposition that was abolished in C1q-deficient serum, indicating transient binding of C1q to bacteria. Moreover, several isolates were recognized by MBL, with C4b deposition abolished in MBL-deficient serum. C3b was deposited on most isolates, but this was not, however, seen with respect to C5b and formation of the membrane attack complex (MAC), indicating that many isolates could avoid complement-mediated lysis. India ink staining showed that isolates were capsulated, and capsule thickness varied significantly between isolates. Studies performed on a wild-type strain and capsule mutant strains, demonstrated that the production of a capsular polysaccharide is one mechanism that mediates resistance to complement-mediated bactericidal activity by preventing MAC deposition and lysis. Our data showed that most clinical Acinetobacter spp. isolates are highly serum resistant despite being efficiently recognized by the complement system.