In response to the presence of endotoxin, phagocytes secrete tumor necrosis factor (TNF). This causes which of the following effects in the host?

• A. Production of antibodies by B cells
• B. Inhibition of neutrophil migration
• C. Fever and increased vascular permeability
• D. Direct lysis of bacterial cells

Answer: (C)

Verified step by step guidance

1. Understand that endotoxins are components of the outer membrane of Gram-negative bacteria that trigger immune responses.
2. Recognize that phagocytes, such as macrophages, respond to endotoxins by secreting cytokines, including tumor necrosis factor (TNF).
3. Recall the biological effects of TNF, which include inducing fever by acting on the hypothalamus and increasing vascular permeability to allow immune cells to access infected tissues.
4. Eliminate options that do not align with TNF's known functions, such as direct lysis of bacterial cells (which is typically done by complement proteins) and inhibition of neutrophil migration (TNF actually promotes neutrophil migration).
5. Conclude that the correct effect of TNF secretion in response to endotoxin is fever and increased vascular permeability.