Immune Responses to Filarial Nematodes: A Mechanistic Evaluation of Evasion and Modulation Strategies

Filarial parasites are long-lived organisms that cause extreme morbidity due to pathological manifestations, including lymphedema, hydrocele, and elephantiasis. Understanding the hosts’ immune responses to filarial parasites is crucial to developing new and effective anti-filarial treatments. The review thoroughly examines and summarises immunological modulation, evasion strategies, and filarial–host immune interactions to provide an updated knowledge of the immune evasion manoeuvres used by filarial parasites. An extensive literature search was conducted using databases such as PubMed, Google Scholar, ScienceDirect, Web of Science, and Scopus to identify articles published mostly between 2000 and 2025 that focus on the crucial molecular, cellular, and immunomodulatory strategies of filarial parasites. The immune evasion mechanisms include the modulation of effector T cells, induction of apoptosis in immune cells, the release of immunomodulatory proteins, and the induction of regulatory immune cell populations, thereby ensuring the mutual survival of both the parasite and the host. An antigen-specific T helper 2 (Th2) response and an increase in Interleukin-10 (IL-10) producing CD4+ T cells, along with a suppressed T helper 1 (Th1) response, are the key immunological characteristics of filarial pathogenesis. This antigen-specific T-cell hyporesponsiveness seems necessary for keeping the long-term infection going, which often involves large parasite densities. This review summarises filarial parasites’ mechanisms and strategies in regulating host immune responses and will facilitate future studies on the filarial pathogenesis, leading to the development of novel anti-filarial therapeutics.