The human complement system is complex, with key components like C1q, C3, and C5 playing essential roles in immune recognition, pathogen lysis, and inflammation. Cleavage products like C3a, C3b, and C5a contribute to opsonization and recruitment of neutrophils. The system's regulation involves factors like CD55 and CD59. (Word count: 49)

Zymogen cascades consist of inactive precursor enzymes called zymogens, which become active through specific cleavage. They are crucial in processes like blood clotting, digestive enzyme activation, and immune response regulation. Positive and negative feedback loops control their activation, and dysregulation can lead to disorders such as hemostatic, inflammatory, and digestive conditions.

The TNF signal transduction pathway plays a vital role in immune response regulation, with a unique positive feedback loop that amplifies the immune response through de novo TNF expression. This loop is perpetuated by autocrine/paracrine signaling and secondary messengers. Negative feedback, such as I-kappa B regulation, prevents excessive inflammation, maintaining immune balance.