The immune system protects the body through two main mechanisms — innate and adaptive immunity. Innate immunity provides the first line of defense using cells like monocytes, macrophages, dendritic cells, and natural killer cells, while adaptive immunity involves T cells, B cells, and antibodies, which provide memory and specificity.

Monocytes play a key role in recognizing infections and can differentiate into macrophages. Two important surface markers, CD169 and CD64, are used to study immune responses. CD169 is upregulated during viral infections and autoimmune conditions, while CD64 increases during bacterial infections. These biomarkers help distinguish between infection types.

Data from the National Family Health Survey- 5 shows improvement in infant and child mortality rates in India compared to NFHS-4, though issues like low birth weight and infectious diseases like pneumonia, diarrhea, malaria, remain major causes of death in children under five.

Accurate diagnosis of infections is crucial to reduce antimicrobial resistance caused by excessive antibiotic use. Traditional methods like blood culture are reliable but slow, so newer markers such as Procalcitonin and C-Reactive Protein, along with leukocyte counts and morphological changes, are used.

A recent study demonstrated that CD64 on neutrophils (nCD64) rises in bacterial infections, while CD169 on monocytes (mCD169) rises in viral infections. These biomarkers show high sensitivity and specificity, making them valuable tools for rapid infection triage and antibiotic stewardship in clinical and epidemic settings.