Acute inflammatory response in the mouse: exacerbation by immunoneutralization of lipocortin 1

1 An immuno‐neutralization strategy was employed to investigate the role of endogenous lipocortin 1 (LC1) in acute inflammation in the mouse. 2 Mice were treated subcutaneously with phosphate‐buffered solution (PBS), non‐immune sheep serum (NSS) or with one of two sheep antisera raised against LC1 (LCS3), or its N‐terminal peptide (LCPS1), three times over a period of seven days. Twenty four hours after the last injection several parameters of acute inflammation were measured including zymosan‐induced inflammation in 6‐day‐old air‐pouches, zymosan‐activated serum (ZAS)‐induced oedema in the skin, platelet‐activating factor (PAF)‐induced neutrophilia and interleukin‐1β (IL‐1β‐induced corticosterone (CCS) release. 3 At the 4 h time‐point of the zymosan inflamed air‐pouch model, treatment with LCS3 did not modify the number of polymorphonuclear leucocytes (PMN) recruited: 7.84 ± 1.01 and 7.00 ± 0.77 × 106 PMN per mouse for NSS‐ and LCS3 group, n = 7. However, several other parameters of cell activation including myeloperoxidase (MPO) and elastase activities were increased (2.2 fold, P < 0.05, and 6.5 fold, P < 0.05, respectively) in the lavage fluids of these mice. Similarly, a significant increase in the amount of immunoreactive prostaglandin E2 (PGE2; 1.81 fold, P < 0.05) and IL‐1α (2.75 fold, P < 0.05), but not tumour necrosis factor‐α (TNF‐α), was also observed in LCS3‐treated mice. 4 The recruitment of PMN into the zymosan inflamed air‐pouches by 24 h had declined substantially (4.13 ± 0.61 × 106 PMN per mouse, n = 12) in the NSS‐treated mice, whereas high values were still measured in those treated with LCS3 (9.35 ± 1.20 × 106 PMN per mouse, n = 12, P < 0.05). A similar effect was also found following sub‐chronic treatment of mice with LCPS1: 6.48 ± 0.10 × 106 PMN per mouse, vs. 2.77 ± 1.20 and 2.64 ± 0.49 × 106 PMN per mouse for PBS‐ and NSS‐treated groups (n = 7, P < 0.05). Most markers of inflammation were also increased in the lavage fluids of LCS3‐treated mice: MPO and elastase showed a 2.47 fold and 17 fold increase, respectively (P < 0.05 in both cases); TNF‐α showed a 11.1 fold increase (P < 0.05) whereas the IL‐1α levels were not significantly modified. PGE2 was still detectable in most (5 out of 7) of the mice treated with LCS3 but only in 2 out of 7 of the NSS‐ treated mice. 5 Intradermal injection of 50% ZAS caused a significant increase in the 2 hoedema formation in the skin of LCS3‐treated mice in comparison to PBS‐ and NSS‐treated animals: 16.7 ± 1.5 μl vs. 10.8 ± 1.2 μl and 10.2 ± 1.0 μl, respectively (n = 14 mice per group, P < 0.05). ZAS‐induced oedema had subsided by 24 h in control animals but a residual significant amount of extravasation was still detectable in LCS3‐ treated mice: 4.4 ± 0.8 μl (P < 0.05). 6 A recently described model driven by endogenous glucocorticoids is the blood neutrophilia observed following administration of PAF. In our experimental conditions, a single bolus of PAF (100 ng, i.v.) provoked a marked neutrophilia at 2 h (2.43 and 2.01 fold) in NSS‐ and PBS‐treated mice (n = 11), respectively, which was significantly attenuated in the animals treated with LCS3: 1.26 fold increase in circulating PMN (n = 11, P < 0.01 vs. NSS‐ and PBS‐groups). 7 Intraperitoneal injection of IL‐1β (5 μg kg−1) caused a marked increase in circulating plasma CCS by 2 h, to a similar extent in all experimental groups. In contrast, measurement of CCS levels in the plasma of mice bearing air‐pouches inflamed with zymosan revealed significant differences between LCS3 and NSS‐treated mice at the 4 h time‐point: 198 ± 26 ng ml−1 vs. 110 ± 31 ng ml−1 (n = 8, P < 0.05). 8 In conclusion, we found a remarkable exacerbation of the inflammatory process with respect to both humoral and cellular components in mice passively immunised against LC1, suggesting the existence of a negative modulatory role for this protein in the normal regulation of the host defence mechanism.