Ans. is 'c' i.e., Lymphocyteo Acute interstitial nephritis (AIN) is a renal lesion that causes decline in creatinine clearance and is characterized by inflammatory infiltrate in the kidney interstitium.o The definitive diagnosis of interstitial nephritis is made by biopsyo The major histological changes are interstitial edema and marked interstitial infiltrate consisting primary of T lymphocyte and monocytes.Eosinophils plasma cells and neutrophils may also be found.The classic lesion of tubulitis is found when inflammatory cells invade the tubular basement membrane.Tubulointerstitial disease -o It is a group of renal disease that is characterized by histological and functional pathology that predominantly involves the tubules and the interstitium.o The primary' function of tubules is reabsorption of salt and water, thus the main symptom of tubulointerstitial disease is impairment in the ability of the kidney to concentrate urine which is clinically manifested as.# Polyuria nocturia# Salt wasting# Diminished ability to excrete acids# Isolated defects in tubular reabsorption or secretiono These are also sometimes called salt wasting nephritis.o These diseases can be easily distinguished from glomerular diseases by their clinical features,o. The hallmark of glomerular diseases clinically are the presence of nephritic and nephrotic syndrome where as the main feature of tubulointerstitial disease is impairment in the ability of kidney to concentrate urine which is manifested as polyuria or nocturia.o These distinctions are prominent in the early stages of the diseases, and advanced form of both the diseases are clinically indistinguishable.Causes of interstitial nephritis; -Drugs (with antibiotic responsible for 1/3 cases) 75%Infections (5-10%)Tubuloiinterstitial nephritis and uveitis (5-10%).Systemic disease including sarcoidosis. Sjogren's syndrome SLE and others(10-15%).