Antibacterial Fusion Proteins Enhance Moraxella catarrhalis Killing

Recent Advances in Immunotherapeutic and Vaccine-Based Approaches for the Treatment of Drug-Resistant Bacterial Infections

Antimicrobial resistance poses a grave threat to global public health. Although new antibiotics are urgently needed, most share resistance mechanisms with existing drugs, thereby necessitating the development of alternative antibacterial therapeutics. Various immunotherapeutic agents, including monoclonal antibodies, therapeutic vaccines, cellular therapies, and immunomodulators, have been developed and explored to treat drug-resistant bacterial infections. This review comprehensively summarizes recent advancements in immunotherapies and vaccine-based approaches as alternative strategies to combat drug-resistant bacterial infections. Our findings indicate that immunotherapy offers several advantages over traditional antibiotics, such as enhanced specificity, long-term effects, overcoming resistance mechanisms, broad applicability, potential for combination therapies, personalized medicine, and reduced toxicity. Also, formulation and delivery strategies, including nanoparticles, liposomes, cellular vehicles, and diverse administration routes, have been employed to improve the efficacy and targeting of these immunotherapeutic agents. In-depth evaluations of promising preclinical and clinical studies demonstrate their potential effectiveness against pathogens such as Pseudomonas aeruginosa, Escherichia coli, Mycobacterium tuberculosis, Streptococcus pneumoniae, methicillin-resistant Staphylococcus aureus, Acinetobacter baumannii, and Helicobacter pylori. These suggest that immunotherapy is a promising alternative to address the growing challenge of drug-resistant bacterial infections, potentially revolutionizing infection management strategies.

Proteomics and Microbiota Conjoint Analysis in the Nasal Mucus: Revelation of Differences in Immunological Function in Manis javanica and Manis pentadactyla

All eight pangolin species, especially captive Manis pentadactyla, are critically endangered and susceptible to various pathogenic microorganisms, causing mass mortality. They are involved in the complement system, iron transport system, and inflammatory factors. M. pentadactyla exhibited a higher abundance of opportunistic pathogens, Moraxella, which potentially evaded complement-mediated immune response by reducing C5 levels and counteracting detrimental effects through transferrin neutralization. In addition, we found that the major structure of C5a, an important inflammatory factor, was lacking in M. javanica. In brief, this study revealed the differences in immune factors and microbiome between M. javanica and M. pentadactyla, thus providing a theoretical basis for subsequent immunotherapy.

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.

Recruitment of C4b-binding protein is not a complement evasion strategy employed by Staphylococcus aureus

Complement offers a first line of defence against infection through the opsonization of microbial pathogens, recruitment of professional phagocytes to the infection site and the coordination of inflammatory responses required for the resolution of infection. Staphylococcus aureus is a successful pathogen that has developed multiple mechanisms to thwart host immune responses. Understanding the precise strategies employed by S. aureus to bypass host immunity will be paramount for the development of vaccines and or immunotherapies designed to prevent or limit infection. To gain a better insight into the specific immune evasion mechanisms used by S. aureus we examined the pathogen's interaction with the soluble complement inhibitor, C4b-binding protein (C4BP). Previous studies indicated that S. aureus recruits C4BP using a specific cell-wall-anchored surface protein and that bound C4BP limits complement deposition on the staphylococcal surface. Using flow-cytometric-based bacterial-protein binding assays we observed no interaction between S. aureus and C4BP. Moreover, we offer a precautionary warning that C4BP isolated from plasma can be co-purified with minute quantities of human IgG, which can distort binding analysis between S. aureus and human-derived proteins. Combined our data indicates that recruitment of C4BP is not a complement evasion strategy employed by S. aureus.

Nontypeable Haemophilus influenzae P5 Binds Human C4b-Binding Protein, Promoting Serum Resistance

Exposure of P5 at the surface of NTHi positively correlates with C4BP binding.

C4BP bound to the bacterial surface retains its complement inhibitory capacity.

C4BP binding to P5 is important for NTHi serum resistance.

Nontypeable Haemophilus influenzae (NTHi) is a Gram-negative human pathogen that causes infections mainly in the upper and lower respiratory tract. The bacterium is associated with bronchitis and exacerbations in patients suffering from chronic obstructive pulmonary disease and frequently causes acute otitis media in preschool children. We have previously demonstrated that the binding of C4b binding protein (C4BP) is important for NTHi complement evasion. In this study, we identified outer membrane protein 5 (P5) of NTHi as a novel ligand of C4BP. Importantly, we observed significantly lower C4BP binding and decreased serum resistance in P5-deficient NTHi mutants. Surface expression of recombinant P5 on Escherichia coli conferred C4BP binding and consequently increased serum resistance. Moreover, P5 expression was positively correlated with C4BP binding in a series of clinical isolates. We revealed higher levels of P5 surface expression and consequently more C4BP binding in isolates from the lower respiratory tract of chronic obstructive pulmonary disease patients and tonsil specimens compared with isolates from the upper respiratory tract and the bloodstream (invasive strains). Our results highlight P5 as an important protein for protecting NTHi against complement-mediated killing.