Sentence:  Microscopically , both kidneys showed many small cortical scars in which there was glomerular and interstitial fibrosis , tubular atrophy , and an infiltration of lymphocytes and <WSD>plasma</WSD> cells . 
Meaning of the word marked with <WSD> tags:  the colorless watery fluid of the blood and lymph that contains no cells, but in which the blood cells (erythrocytes, leukocytes, and thrombocytes) are suspended