Inflammatory cells invading islets are thought to be mediators of islet destruction
in spontaneous autoimmune diabetes mellitus. Thus methods were developed to isolate
and characterize in situ islet inflammatory cells from 75-95-day-old prediabetic and
diabetic BB rats. Islet inflammatory cells were structurally examined using single-
and double-colour flow cytometry. Functional studies consisted of cytolytic assays
using normal rat islet target cells and in situ islet or spleen effector cells. Structural
data reveal natural killer cells to be the major cell population (70%) of total immune
cells present in inflamed islets during prediabetes. At diabetes onset, the natural
killer cell population remained at a high level (47%), but an increasing population
of T cells (40%) was noted also. Analyses of T-cell subsets before and after diabetes
onset revealed CD4+ T cells as predominant (50-55% of total T cells) with double-negative
(CD4- CD8-) T cells (25-30%) and CD8- T cells (15-20%) also present in significant
quantities. Activated T cells accounted only for a minority of T cells (< 3% ). Functional
studies indicate that in situ islet-derived cytolytic effector cells are more potent
killers (ten-fold) of normal islet target cells than are splenic effector cells. These
data suggest that in situ islet inflammatory cells (a) can be quantitatively studied
both structurally and functionally; (b) express structural phenotypes differing substantially
from splenic mononuclear cell populations; (c) are considerably more cytolytic than
splenic effectors; and (d) should prove informative in determining the most significant
autoimmune functional events prior to and during islet beta-cell destruction.
