In MRL/Mp-lpr/lpr (MRL/lpr) and MRL/Mp-+/+ (MRL/+) mice, a T-cell-driven lacrimal gland inflammation spontaneously develops that is a model for Sjögren's syndrome. The lacrimal gland lesions in these mice were evaluated by immunohistochemistry for the relative contributions of T-helper (Th)1 versus Th2 immune responses.Frozen sections of lacrimal glands from MRL/lpr and MRL/+ mice ages 1 through 5 months were stained with monoclonal antibodies to the cytokines interferon (IFN)-gamma and interleukin (IL)4 and to the cell surface costimulatory molecules B7-1 and B7-2, which are associated with Th1 and Th2 responses, respectively.The median proportion of cells staining for IL-4 ranged from 30% to 67% over time for MRL/lpr mice and from 30% to 55% for MRL/+ mice. The median proportion of cells staining for IFN-gamma ranged from 1% to 5% for MRL/lpr mice and from 0% to 3% for MRL/+ mice. The proportion of cells staining positively for IL-4 was significantly greater than for IFN-gamma in both MRL/lpr (mean difference, 33%; P = 0.0001) and MRL/+ mice (mean difference, 42%; P = 0.0002). The median proportion of cells staining positively for B7-2 ranged from 20% to 38% for MRL/lpr mice and from 16% to 34% for MRL/+ mice. The median proportion of cells staining for B7-1 ranged from 2% to 10% for MRL/lpr mice and from 2% to 5% for MRL/+ mice. The proportion of cells staining positively for B7-2 was significantly greater than for B7-1 for both MRL/lpr mice (mean difference, 15%; P = 0.001) and for MRL/+ mice (mean difference, 19%; P = 0.006).On the basis of immunohistochemistry for cytokines and costimulatory molecules, inflammatory lacrimal gland lesions in MRL/lpr and MRL/+ mice appear to be a largely Th2 phenomenon.