Which of the following statements are correct?

I. Allergy refers to an exaggerated immune response to specific antigens present in the environment.

II. The tendency to develop allergies is inherited from parents and is characterized by high levels of IgG antibodies in the bloodstream.

III. Lymphocytes originate, mature, and proliferate in the bone marrow and thymus.

IV. Subsequent encounter with the same pathogen for the second time elicits a highly intensified secondary immune response.

I, III and IV

The correct answer is Option (3) -I, III and IV

I. Allergy refers to an exaggerated immune response to specific antigens present in the environment.

Correct. Allergies occur when the immune system overreacts to harmless substances (antigens) like pollen, dust, or certain foods, treating them as harmful invaders.

II. The tendency to develop allergies is inherited from parents and is characterized by high levels of IgG antibodies in the bloodstream.

Incorrect. Allergic tendency can be genetically passed from the parents to their offspring and is characterised by the presence of large quantities of IgE antibodies in the blood.

III. Lymphocytes originate, mature, and proliferate in the bone marrow and thymus.

Correct. Lymphocytes, such as T cells and B cells, originate in the bone marrow. T cells mature in the thymus, while B cells mature in the bone marrow itself.

IV. Subsequent encounter with the same pathogen for the second time elicits a highly intensified secondary immune response.

Correct. This is known as the secondary immune response, where memory cells trigger a faster and more potent reaction upon re-exposure to the same pathogen, leading to stronger immunity.

So, the correct statements are I, III, and IV.