Human plasma cells (PC) are present in cell suspensions obtained from the tonsil by mechanical disaggregation (PC(MECH)). The present study shows that a collagenase treatment of tonsillar debris remaining after mechanical disaggregation yielded similar proportions of PC (PC(COLL)). Moreover, PC(MECH) were present in suspensions highly enriched in germinal center cells whereas PC(COLL) contained most of the IgA-secreting cells, suggesting their predominant location in follicular and parafollicular areas and connective tissue-rich zones such as tonsil subepithelium, respectively. Tonsil PC(MECH) and PC(COLL) shared the phenotype CD38(high) CD19(+) CD20(low) CD45(high), expressed equivalent amounts of PRDI BF1/Blimp-1 transcription factor, and carried similarly mutated IgVH6 genes. However, they differed in several features. 1) PC(MECH) still expressed the early B cell transcription factor BSAP and were HLA-DR(high); in contrast, PC(COLL) were BSAP(-)and HLA-DR(low). 2) PC(MECH) were CD95(+) and Bcl-2(+/-) whereas PC(COLL) showed CD95(+/-) and Bcl-2(+) expression; in addition, PC(MECH) exhibited increased spontaneous apoptosis. 3) The two PC subsets exhibited distinctive adhesion molecule profiles, since PC(COLL) expressed higher levels of CD31, CD44, and CD49d, but a lower level of CD11a than PC(MECH). These results suggest that PC(MECH) are recently generated, short-living PC, and PC(COLL) constitutes a subset with higher maturity and survival, which resides in connective tissue-rich areas.