The language of the immune system: Part 1: Cytokine conversations and conversationalists

The immune system is always acting to protect the body from the microbial world, especially at the openings of the body but also helps to maintain homeostasis. Normal functions include self-regulation and regeneration, facilitating the maintenance of organs, skin and mucosal membranes, protecting the openings of the body, providing surveillance for abnormal and cancer cells and eliminating molecular and cellular debris. In addition to status quo maintenance functions, the immune system responds to damage, disruption or danger when challenged by trauma, infection, cancer, autoimmunity and other diseases. The responses are communicated and coordinated to other cells, tissues, organs, and systems through cell-cell interactions, with different soluble molecules including cytokines. Cytokines are the language of the immune system and define the progression of the subsequent immune response. Each cytokine may elicit its own responses but by acting together in a conversation they communicate and coordinate the intended actions to maintain the status quo or respond to challenge. These conversations include regulation/tolerance, alarmins, acute phase cytokines, Th1, Th2, Th17, and Th22. The cytokine conversations, their conversationalists (the cells eliciting and responding to cytokines), and the basic responses of the immune system will be discussed. An easy way to remember the conversations is provided.