**Question:** Opsonisation is by -

A. Complement activation
B. Antibody binding
C. Phagocyte receptors
D. Degranulation of mast cells

**Core Concept:** Opsonisation is a crucial process in the immune system that enhances the ability of phagocytic cells (e.g., macrophages, neutrophils) to engulf and destroy pathogens such as bacteria and viruses. This process is achieved through complement activation, antibody binding, and recognition by phagocyte receptors.

**Why the Correct Answer is Right:** Opsonisation involves the attachment of opsonins (proteins or antibodies) to the surface of pathogens, which enhances their recognition and phagocytosis by phagocytic cells. Complement activation (option A) and antibody binding (option B) are key steps in the opsonisation process, as they facilitate the attachment of opsonins to the pathogen surface. Phagocyte receptors (option C) recognize and bind to these opsonins, leading to the engulfment and destruction of the pathogen.

**Why Each Wrong Option is Incorrect:**

- Degranulation of mast cells (option D) is a process involved in allergic reactions and does not directly contribute to the immune response against pathogens.

**Correct Answer:**

**Answer:** A and B (Complement activation and Antibody binding)

**Clinical Pearl:** Opsonisation is a critical mechanism that helps the immune system recognize and eliminate pathogens efficiently, highlighting the importance of complement activation, antibody binding, and phagocyte receptors in this process. Understanding these components can aid in interpreting laboratory findings and clinical outcomes related to immune deficiencies or dysfunctions in these pathways.