The complement cascade and Neutrophil Extracellular Traps (NETs) represent fundamental tools in protecting the host from foreign pathogens. Complement components and relative fragments, classically assigned to the innate immunity, represent a key link with the humoral immune response. NETs are a crucial component of the innate immune response, consisting of chromatin release from activated neutrophils. These web-like structures facilitate pathogen entrapment and elimination through proteolytic degradation and antimicrobial effectors. Previous findings suggested complement components and NETs have a significant role in the pathogenesis of several diseases characterized by inflammation, such as autoimmune and infectious diseases. However, the crosstalk between NETs and the complement cascade has only recently been investigated, and several aspects still need to be fully clarified. Recent evidence seems to suggest a bidirectional link between the complement cascade and NETosis. We here present the interaction between complement components and NETs in specific autoimmune diseases that mostly affect the kidney, such as systemic lupus erythematosus, Antineutrophilic Cytoplasmic Antibody (ANCA)-associated vasculitis and antiphospholipid syndrome. The mechanisms reported here may represent specific targets for the development of possible therapeutic strategies.

Background.: Focal segmental glomerulosclerosis (FSGS) recurrence after kidney transplantation is a leading cause of allograft failure and remains difficult to treat. Standard therapies, including plasma exchange (PEX) and rituximab, are often ineffective and poorly tolerated. Growing evidence implicates immune-mediated circulating factors, such as IgG and IgM autoantibodies, in disease pathogenesis. Given the central role of memory B cells and plasma cells in antibody production, we tested the safety/efficacy profile of a combined B-cell and plasma cell–depleting approach with rituximab and daratumumab in patients with posttransplant FSGS recurrence. Methods.: This is a retrospective analysis of a multicenter, international cohort of sixteen patients (median age 37 y) with biopsy-proven FSGS recurrence posttransplant who received anti-CD20 plus anti-CD38 monoclonal antibodies or anti-CD38 alone. The majority of patients were resistant to common therapies, including rituximab and PEX. Results.: The treatment achieved complete or partial remission in 5 and 11 patients, respectively. Five experienced proteinuria relapse, and 4 responded to repeated daratumumab alone. At the last follow-up (median 11 [2–18] mo), 13 patients are still in remission and PEX was discontinued in all but 3 cases. Overall, kidney function improved after treatment, and no severe acute or chronic adverse events were reported. Serological analysis revealed a significant decline in IgM, but not in IgG, after treatment. Conclusions.: Despite the retrospective, nonrandomized design, the temporal association between treatment and remission supports an effect of anti-CD38 monoclonal antibody alone or in combination with anti-CD20. Treatment is safe and may confer enhanced efficacy over standard approaches. Prospective, mechanistic studies are warranted to validate these findings and delineate the immunopathogenesis of FSGS recurrence.

Immunoglobulin A nephropathy represents the most prevalent cause of glomerulonephritis worldwide and may lead to renal failure in a relevant number of cases in both paediatric and adult subjects. Although their pathogenesis is still largely unclear, evidence of immune abnormalities provides the background for the use of immunosuppressive drugs, such as corticosteroids, calcineurin inhibitors, and antiproliferative and alkylating agents. Unfortunately, these treatments fail to achieve a sustained remission in a significant percentage of affected patients and are burdened by significant toxicities. Recent developments of new biologics, including anti-BAFF/APRIL inhibitors and molecules targeting complement components, offered the opportunity to selectively target immune cell subsets or activation pathways, leading to more effective and safer hypothesis-driven treatments. However, studies testing new biologic agents in IgAN should also consider paediatric populations to address the unique needs of children and close the therapeutic gap between adult and paediatric care.

Background/Objectives: Atypical hemolytic uremic syndrome (aHUS) is a rare, life-threatening thrombotic microangiopathy caused by dysregulation of the alternative complement pathway, often related to genetic mutations or autoantibodies. The introduction of complement C5 inhibitors, such as eculizumab and ravulizumab, has significantly improved renal and overall outcomes. However, complement inhibition impairs host defense against encapsulated bacteria, markedly increasing the risk of invasive infections, particularly Neisseria meningitidis. Vaccination against meningococcal groups ACWY and B, along with temporary antibiotic prophylaxis, is therefore recommended before initiating anti-C5 therapy. Methods: We report the clinical course of a 13-year-old boy with aHUS secondary to anti–complement factor H (CFH) autoantibodies and CFHR3–CFHR1 homozygous deletion, treated with C5 inhibitors. Results: Despite complete meningococcal vaccination and a previous course of antibiotic prophylaxis, the patient developed meningitis during ongoing complement inhibitor therapy. Conclusions: This case highlights that breakthrough invasive infections may occur despite adherence to recommended preventive strategies. It underscores the need for sustained clinical vigilance, timely vaccine boosters, and careful reassessment of the risk–benefit balance of continued complement inhibition therapy.