Altered cytokine production, but not activation marker expression, by Syk-deficient neutrophils in the arthritic joint. A, B, Ly6G+ Neutrophils were isolated from the peripheral blood and synovial fluid of arthritic mixed bone marrow chimeras on day 7 following K/BxN serum transfer and stained for CD11b and CD62L (L-selectin). Mean fluorescence intensity of CD11b and CD62L for Syk-deficient (CD45.2+, white bars) or wild type (CD45.1+ gray bars) neutrophils are shown compared to peripheral blood neutrophils from a control B6 mouse not treated with serum (black bars). C, Day 7 synovial fluid neutrophils from mixed chimeric mice were stained with Ly6G, annexin V and propidium iodide (PI) and the percentage of positive cells for each marker are shown. A-C, n=7. D, Day 7 synovial fluid neutrophils were pooled from 8 mixed chimeric mice and stained for intracellular TNFα as described in Materials and Methods following 6 hours of incubation with media or media plus immune complexes (indicated as IC) or media plus 10 ng/ml LPS. Wild type versus sykf/f MRP8-cre+ cells were distinguished by CD45.1 versus CD45.2 staining. E, F, Naïve bone marrow neutrophils were isolated from either wild type or syk−/− fetal liver chimeric mice and stimulated in vitro with the indicated agonists for 6 hours, then E, stained for intracellular TNFα or F, culture supernatant was collected for TNFα ELISA as described in Materials and Methods (n = 3). Statistics analyzed by two-way ANOVA. IC = insoluble immune complex. *=p<0.05, **=p<0.01, *** = p<0.001