The function of IgE is:

Options

A. activation of B-cells
B. mediate in allergic response
C. present on lymphocyte surface as receptors
D. protection from inhaled and ingested pathogens

Answer

To determine the function of IgE, let's analyze each option provided in the question step by step.

### Step 1: Evaluate the first option - Activation of B cells
- **Analysis**: The activation of B cells is primarily associated with IgD immunoglobulin. Therefore, this option is incorrect.
- **Hint**: Remember that IgD is specifically involved in the activation of B cells.

### Step 2: Evaluate the second option - Mediate in allergic responses
- **Analysis**: IgE is known for its role in mediating allergic responses. It binds to allergens and triggers histamine release from mast cells and basophils, leading to inflammation and allergy symptoms. This option is correct.
- **Hint**: Think about how allergies manifest and the role of IgE in that process.

### Step 3: Evaluate the third option - Presence of lymphocyte surface as receptor
- **Analysis**: The receptors present on lymphocytes are primarily Major Histocompatibility Complex (MHC) molecules, not IgE. Thus, this option is incorrect.
- **Hint**: MHC molecules are crucial for antigen presentation, not IgE.

### Step 4: Evaluate the fourth option - Protection from inhaled and ingested pathogens
- **Analysis**: Protection from inhaled and ingested pathogens is mainly provided by phagocytes and other immune cells, not IgE. Therefore, this option is also incorrect.
- **Hint**: Consider which immune cells are primarily responsible for protecting against pathogens.

### Step 5: Evaluate the last option - Stimulation of complement system, passive immunity to phytos
- **Analysis**: IgE does not stimulate the complement system; that role is more associated with IgM and IgG. Additionally, while IgE can cross the placenta, it is not primarily known for providing passive immunity. This option is incorrect.
- **Hint**: Recall which immunoglobulins are known for complement activation and passive immunity.

### Conclusion
After evaluating all the options, the correct function of IgE is to mediate allergic responses. Therefore, the answer is:

**Correct Answer: Mediate in allergic responses (Option B)**