Identify an immunoglobulin present in milk, saliva and tears.

Appeared in: DSSSB -28 August 2019 (Shift-2)

Explanation

IgA is the primary antibody class found in mucosal secretions.
These secretions include milk (especially colostrum), saliva, tears, and mucus of the respiratory and intestinal tracts.
In secretions, it exists as a dimer called secretory IgA, which is resistant to enzymatic digestion.
Its main function is to provide local or mucosal immunity, acting as the first line of defense by neutralizing pathogens on mucosal surfaces.

Option A: IgG is the most abundant immunoglobulin in the blood serum and extracellular fluid, not in secretions.
Option B: IgM is primarily found in the bloodstream and is the first antibody to appear in response to an initial infection. It is too large to pass into most secretions.
Option D: IgE is found in very low concentrations and is primarily associated with allergic reactions (Type I hypersensitivity) and defense against parasitic worms.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Types and functions of immunoglobulins as background academic context rather than a clinical decision trigger.
The presence of secretory IgA in breast milk is a key reason why breastfeeding is recommended to protect newborns from gastrointestinal and respiratory infections.
Selective IgA deficiency is the most common primary immunodeficiency. Patients may be asymptomatic or suffer from recurrent sinopulmonary and gastrointestinal infections.
What if? If a newborn is not breastfed, they miss out on the passive immunity conferred by maternal IgA. This makes them more susceptible to infections like diarrhea and pneumonia in the early months of life.

How to Approach the Question

First, identify the keywords in the question: 'immunoglobulin', 'milk', 'saliva', and 'tears'. These point to secretions.
Next, recall the primary locations and functions of the different immunoglobulin classes (IgG, IgM, IgA, IgE).
Associate IgG with blood and placental transfer.
Associate IgM with the primary immune response in the blood.
Associate IgA with mucosal secretions.
Associate IgE with allergies.

Concept Tested & Keywords

QO09w5PuxDMx6xVIs85r7R

E6 Microbiology Essentials Sastry 4e Part 1 p. 149-151

E6 Biochemistry U Satyanarayana— Part 2 (pp 421-820 of 840) p. 348-350

E6 Microbiology Applied AnjuDhir 3e Part 2 p. 94-96

Practise the full DSSSB -28 August 2019 (Shift-2)

Attempt every question from this paper in a timed mock, then review the full solution for each one.