What is HLA?

Options

A. Group og genes
B. Group of proteins
C. Group of polypeptides
D. Group of chromosomes

Answer

### Step-by-Step Solution:

1. **Understanding HLA**: HLA stands for Human Leucocyte Antigen. It is essential to know the full form to grasp its significance in immunology.

2. **Identifying HLA as a Group of Genes**: HLA is primarily recognized as a group of genes. These genes are crucial because they encode proteins that play a vital role in the immune response.

3. **Connection to Major Histocompatibility Complex (MHC)**: The proteins encoded by HLA genes are part of the Major Histocompatibility Complex (MHC). MHC molecules are cell surface proteins that are essential for the immune system to recognize foreign molecules.

4. **Role in Immune Response**: When an antigen (a foreign substance) enters the body, MHC proteins present these antigens to T helper cells and cytotoxic T cells. This presentation is crucial for the activation of the immune response, allowing the body to detect and eliminate the antigen.

5. **Evaluating Other Options**:
- The second option mentions "group of proteins," which is misleading because HLA refers to genes that encode proteins, not proteins themselves.
- The third option states "group of polypeptides," which is also incorrect for the same reason.
- The last option, "group of chromosomes," is incorrect since HLA is not a group of chromosomes but rather a set of genes located on specific chromosomes.

6. **Conclusion**: The correct answer is that HLA is a group of genes that encode proteins involved in the immune response.