Among the five classes of immunoglobulins in humans, the one that is secretory in nature is

Options

A. Ig A
B. Ig E
C. Ig M
D. Both a and c

Answer

To solve the question regarding which class of immunoglobulin in humans is secretory in nature, we can follow these steps:

### Step 1: Identify the Classes of Immunoglobulins
There are five major classes of immunoglobulins (Ig) in humans:
1. Immunoglobulin A (IgA)
2. Immunoglobulin D (IgD)
3. Immunoglobulin E (IgE)
4. Immunoglobulin M (IgM)
5. Immunoglobulin G (IgG)

### Step 2: Understand the Function of Each Class
- **IgA**: Primarily found in secretions such as mucus, saliva, tears, and breast milk. It plays a crucial role in mucosal immunity.
- **IgD**: Functions mainly as a receptor on B cells; its exact role is not well understood.
- **IgE**: Involved in allergic responses and protection against parasitic infections. It binds to mast cells and basophils.
- **IgM**: The first antibody produced in response to an infection; it is pentameric and plays a role in the primary immune response.
- **IgG**: The most abundant antibody in circulation, involved in the secondary immune response.

### Step 3: Identify the Secretory Immunoglobulin
From the functions described:
- **IgA** is the only immunoglobulin that is secretory in nature, as it is present in various bodily secretions.

### Step 4: Eliminate Incorrect Options
- **IgE** is not secretory; it is involved in allergic reactions.
- **IgM** is not considered a secretory antibody; it is primarily involved in the initial immune response.
- The option "both A and C" is incorrect since IgC (which is not a class) is not relevant.

### Conclusion
The correct answer to the question is **Immunoglobulin A (IgA)**, as it is the only immunoglobulin that is secretory in nature.

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