STANDARDIZATION OF MEASUREMENT OF IMMUNOGLOBULIN-SECRETING CELLS IN HUMAN PERIPHERAL-CIRCULATION

A sensitive, and at times the most sensitive, measurement of human vac cine immunogenicity is enumeration of antibody-secreting cells (ASC) i n peripheral blood. However, this assay, which is inherently capable o f measurement of the absolute number of antigen-specific ASC, is not s tandardized, Thus, quantitative comparison of results between laborato ries is not currently possible, To address this issue, isotype-specifi c ASC were enumerated from paired fresh and cryopreserved mononuclear cell (MNC) preparations from healthy adult volunteers resident in eith er the United States (US group) or Egypt (EG group). Analysis of fresh cells from US volunteers revealed mean numbers of ASC per 10(6) MNC o f 617, 7,738, and 868 for immunoglobulin M (IgM), IgG, and IgA, respec tively, whereas EG volunteers had 2,086, 7,580, and 1,677 ASC/10(6) MN C for the respective isotypes. Cryopreservation resulted in a slight r eduction in group mean IgM, IgG, and IgA ASC (maximum reduction in gro up mean, 14%), but in no instance were results obtained with cryoprese rved cells significantly lower than those obtained with fresh cells. T o determine if cryopreservation affected the number of bacterial antig en-specific ASC detected, cells from a group of US adult volunteers wh o received a single oral dose of a mutated Escherichia coli heat-labil e enterotoxin (LTR192G) were tested, There was no significant differen ce (P > 0.05) in the number of antigen-specific IgA or IgG ASC detecte d between fresh and cryopreserved MNC. The results support the views t hat ASC assays can be standardized to yield quantitative results and t hat the methodology can be changed to make the test more practical.