Natural killer cells which are also called NK cells are cytotoxic lymphocytes that are different from B cells (B lymphocytes) and T cells (T lymphocytes). These natural killer cells degrade the cells which are infected by intracellular pathogens or cancer cells. A T-cytotoxic cell is T lymphocyte which kills cancerous cells or cells infected with viruses.

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Chapter 26.10, Problem 1CR

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Natural killer cells which are also called NK cells are cytotoxic lymphocytes that are different from B cells (B lymphocytes) and T cells (T lymphocytes). These natural killer cells degrade the cells which are infected by intracellular pathogens or cancer cells. A T-cytotoxic cell is T lymphocyte which kills cancerous cells or cells infected with viruses.

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B cells express a complement receptor that binds to C3b cleavage products, such as iC3b and C3dg. When a B cell with an antigen receptor that specifically recognizes that pathogen also has its complement receptor stimulated because the pathogen is opsonized with these C3 fragments, B cell activation is greatly enhanced. Due to this mechanism, B cells can be activated by much lower concentrations of antigen (in this case, the pathogen) than if the antigen is devoid of complement components. This mechanism functions to: Ensure that pathogens are readily detected by the adaptive immune system before they replicate to high levels in the host Prevent B cells from being activated in response to antigens that are not pathogens Allow B cells to phagocytose the pathogen and help destroy it Induce increased rounds of B cell replication to make more pathogen-specific B cells Allow the B cell to block pathogen replication by interfering with multiple pathogen surface functions

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Opsonization of pathogens by both antibodies and complement proteins (C3b) leads to uptake and destruction of the pathogen by phagocytic cells that express both Fc receptors and complement receptors. Which of the following in the figure below is the most efficient form of dual opsonization of the pathogen by antibody and C3b to maximize phagocytosis?