**Question:** Immunity that is conferred to the foetus by the passage of IgG and IgA antibodies is called as:

A. Maternal immunity
B. Passive immunity
C. Active immunity
D. Natural immunity

**Core Concept:** Passive immunity is a type of immunity that is acquired by an individual without being exposed to the actual pathogen. This immunity is acquired through the circulation of antibodies in the blood or other body fluids, such as breast milk. In the case of a pregnant woman, the antibodies passed on to the foetus via the placenta and amniotic fluid provide protection against certain infections before the baby is born.

**Why the Correct Answer is Right:** The correct answer, **B. Passive immunity**, is right because it refers to the immunity acquired passively, meaning it is not produced by the individual but rather acquired from an external source, in this case, the mother. The passage of antibodies from the mother to the foetus is a form of passive immunity.

**Why Each Wrong Option is Incorrect:**

A. Maternal immunity (option A) is a broader term that includes not only the immunity acquired passively but also the immunity acquired actively through exposure to pathogens. However, in this case, we are specifically discussing the passive immunity passed from mother to foetus.

B. Active immunity (option C) refers to the immunity acquired by the individual through direct exposure to pathogens or immunization, which is not the type of immunity described in this question.

D. Natural immunity (option D) is also a broader term that includes both active and passive immunity. However, as mentioned earlier, this question specifically addresses the passive immunity passed from mother to foetus.

**Clinical Pearl:** The passive immunity provided by maternal antibodies can be crucial for the baby's protection, particularly during the first few months of life when the baby's own immune system is developing. This protection helps prevent severe infections and illnesses in newborns, allowing the baby to build up its own immunity gradually.

**Explanation:**

* **B. Passive immunity** is crucial for the baby's protection during the initial stages of life when the baby's own immune system is developing. This immunity is provided by the antibodies passed from the mother to the foetus via the placenta and amniotic fluid. The maternal antibodies help prevent severe infections and illnesses in newborns, allowing them to develop their own immunity gradually.

**Core Concept:** Passive immunity is a type of immunity that is acquired by an individual without active exposure to antigens, either through the circulation of antibodies from another individual (as in the case of maternal antibodies passing to the foetus) or through immunoglobulins administered through immunization (e.g., through vaccines).

**Why Each Wrong Option is Incorrect:**

A. **Maternal immunity (option A)** includes both passive and active immunity, not specifically addressing the type of immunity provided by the maternal antibodies passing to the foetus.

C. **Active immunity (option C)** refers to immunity acquired through direct exposure to antigens, which is not the type of immunity discussed in this question.

D. **Natural immunity (option D)** is another broad term