Question 1: ABO antigens are not found in:
- A. Semen
- B. CSF (Correct Answer)
- C. Saliva
- D. Tears
Explanation: ***CSF***
- ABO antigens are typically expressed on the surface of **red blood cells** and in the secretions of individuals classified as **secretors**.
- **Cerebrospinal fluid (CSF)** is generally devoid of these antigens.
*Semen*
- ABO antigens can be found in **semen**, particularly in individuals who are secretors.
- This is due to the presence of **secreted bodily fluids** containing soluble forms of these antigens.
*Saliva*
- **Saliva** is a well-known source of soluble ABO antigens in secretor individuals.
- The presence of these antigens in saliva is often used in **forensic testing** and blood group determination.
*Tears*
- Similar to other bodily secretions, **tears** can contain soluble ABO antigens in secretor individuals.
- This is part of the general secretion of these antigens into exocrine fluids.