Peptides and peptidomimetics as immunomodulator agents targeting neglected tropical diseases.

The human immune system is a highly integrated and dynamic network designed to detect, respond to, and eliminate a wide range of infectious agents while preserving tissue homeostasis. This chapter provides an overview of the fundamental organization and function of innate and adaptive immunity, followed by a focused description of the human infection cycles of major pathogens of global health relevance, including Trypanosoma brucei (human African trypanosomiasis), T. cruzi (Chagas disease), Leishmania spp., Schistosoma mansoni, Plasmodium spp., and arboviruses such as Zika and dengue viruses. Emphasis is placed exclusively on the stages of each life cycle that occur within the human host, highlighting key cellular niches, tissue tropisms, and host-pathogen interactions that shape disease progression. In addition, the chapter discusses the diverse immunomodulatory strategies employed by these pathogens to evade immune detection, subvert effector mechanisms, and establish persistent or chronic infections. These mechanisms include antigenic variation, immune cell dysfunction, cytokine skewing, regulatory pathway activation, and molecular mimicry. By integrating immunological principles with pathogen-specific infection dynamics, this chapter aims to provide a coherent framework for understanding how immune responses are initiated, regulated, and manipulated during infection. Such knowledge is essential for the rational design of vaccines, immunotherapies, and host-directed interventions against parasitic and viral diseases.