Endocrine Immune Interactions in the Host-Parasite Relationship: SteroidHormones as Immune Regulators in Parasite Infections

Abstract

There is a close relationship between hormones, cytokines, neuropeptides, and neurotransmitters that modulate the host immune response by several effector mechanisms, including both cellular and humoral immunity. Disruption of this communication balance results in disease or in a higher susceptibility to infections. The relationships between parasites and hosts are complex and there is substantial interaction, communication and biochemical co-evolution. The role of certain hormones in parasitic infections has been demonstrated, and there are documented direct effects of hormones on parasites. Many parasites induce the secretion of molecules that influence the physiological and immunological responses in hosts, including intermediaries and vectors. Conversely, the parasites secrete many factors that alter hormone host levels. In some cases, hormones have positive or negative effects on the parasites status. In other cases, effects are mediated indirectly via the host’s immune system. In vertebrates, the parasite presence also has a major influence on the host’s endocrine status and the normal suite of processes governed by hormones. These processes include host development, establishment, metamorphosis, and reproduction. Thus, understanding the mechanisms involved in immunoendocrine modulation and its effects on parasites is essential for developing new drugs, finding vaccine targets and devising new therapies for several infectious diseases.