Humans have species resistance to feline immunodeficiency virus (FIV) for which of the following reasons?

• A. FIV is rapidly destroyed by human stomach acid before infection can occur.
• B. Human cells lack the specific receptors required for FIV entry.
• C. Humans produce antibodies that immediately neutralize FIV upon exposure.
• D. Human immune cells recognize FIV as a self-antigen and do not mount a response.

Answer: (B)

Verified step by step guidance

1. Understand the concept of species resistance, which refers to the natural ability of a species to resist infection by a pathogen that typically infects another species.
2. Recognize that viral infection generally requires the virus to bind to specific receptors on the host cell surface to gain entry and initiate infection.
3. Identify that feline immunodeficiency virus (FIV) infects cats by binding to receptors unique to feline cells, which are absent on human cells.
4. Evaluate the options given: destruction by stomach acid is a general barrier but not the primary reason for species resistance; immediate antibody neutralization requires prior exposure, which is unlikely; recognition as self-antigen would prevent immune response, not infection.
5. Conclude that the key reason humans have species resistance to FIV is because human cells lack the specific receptors required for FIV to enter and infect the cells.