Longevity of immune complexes and abnormal germinal centre formation in NZB mice

Rheumatoid factor (RF)-like (antibody-antibody) immune complexes induce a selective and intensive immunoglobulin (Ig)G1-RF response after a single injection in mice. However, the longevity of the response differs between mouse strains: serum IgG1-RF antibody titres decline 40 days after injection in C57Bl/6 mice whereas levels are maintained for more than 100 days in NZB mice. In order to elucidate whether this difference was owing to a lower ability of NZB mice to clear the injected immune complexes, sections of kidney, spleen, liver and mesenteric lymph nodes were harvested at different time points after injection with RF-like immune complexes. Immunohistochemical staining revealed that NZB mice have a delayed clearance of the injected immune complexes, because the immune complexes are retained for more than 40 days in their spleens and 100 days in their kidneys, compared to only 14 days in C57Bl/6 mice. Germinal centres were also present for a longer period in the spleens of the NZB mice, accompanying the presence of the immune complexes, and were abnormally large compared to C57Bl/6 mice. The clearance of immune complexes from the spleen coincided with the decline in serum levels of IgG1-RF, indicating that prolonged retention of immune complexes is responsible for the sustained IgG1-RF response.