Select the incorrect statement.

Options

A. The T - lymphocytes mediate CMI.
B. The body is able to differentiate 'self' and 'non-self' and the humoral immune response is responsible for graft rejection
C. The foetus also receives some antibodies from their mother through the placenta during preganancy
D. Each antibody molecule has four peptide chains, two small called light chains and two longer called heavy chains.

Answer

To solve the question of identifying the incorrect statement regarding the immune system, we will analyze each statement provided in the question step by step.

### Step 1: Understanding the Immune System
The immune system is divided into two main responses:
1. **Humoral Immune Response**: This involves B-lymphocytes that produce antibodies to fight pathogens.
2. **Cell-Mediated Immune Response (CMI)**: This involves T-lymphocytes that help in recognizing and destroying infected or foreign cells.

**Hint**: Remember the two types of immune responses and their associated lymphocytes.

### Step 2: Analyzing the Statements
Now we will evaluate the statements one by one:

- **Statement A**: "T-lymphocytes are responsible for humoral immune response."
- This statement is incorrect because T-lymphocytes are involved in cell-mediated immunity, not humoral immunity.

**Hint**: Identify which lymphocytes are responsible for which type of immune response.

- **Statement B**: "The body can differentiate between self and non-self due to humoral immunity."
- This statement is incorrect. The ability to differentiate between self and non-self is primarily due to cell-mediated immunity, not humoral immunity.

**Hint**: Focus on the role of T-lymphocytes in recognizing self vs. non-self.

- **Statement C**: "The fetus receives antibodies from the mother through the placenta."
- This statement is correct. The mother transfers antibodies to the fetus, providing passive immunity.

**Hint**: Recall how antibodies are transferred from mother to child.

- **Statement D**: "In every antibody molecule, there are 4 peptide chains: 2 light chains and 2 heavy chains."
- This statement is also correct. Antibodies are composed of two types of chains.

**Hint**: Remember the structural components of antibodies.

### Step 3: Identifying the Incorrect Statement
From the analysis:
- Statement A is incorrect regarding T-lymphocytes and humoral immunity.
- Statement B is also incorrect regarding the differentiation of self and non-self.

However, the question asks for the incorrect statement, and since both A and B are incorrect, we need to choose the one that is more explicitly wrong in the context provided.

### Conclusion
The incorrect statement is:
**Statement B**: "The body can differentiate between self and non-self due to humoral immunity."

### Final Answer
**Option B** is the incorrect statement.