Novel lymphotoxin alpha (LTα) knockout mice with unperturbed tumor necrosis factor expression:: Reassessing LTα biological functions

Lymphotoxin alpha (LT alpha) can exist in soluble form and exert tumor necrosis factor (TNF)-like activity through TNF receptors. Based on the phenotypes of knockout (KO) mice, the physiological functions of LT alpha and TNF are considered partly redundant, in particular, in supporting the microarchitecture of the spleen and in host defense. We exploited Cre-LoxP technology to generate a novel neomycin resistance gene (neo) cassette-free LT alpha-deficient mouse strain (neo-free LT alpha KO [LT alpha(Delta/Delta)]). Unlike the conventional LT alpha(-/-) mice, new LT alpha(Delta/Delta) animals were capable of producing normal levels of systemic TNF upon lipopolysaccharide (LPS) challenge and were susceptible to LPS/D-galactosamine (D-GaIN) toxicity. Activated neutrophils, monocytes, and macrophages from LT alpha(Delta/Delta) mice expressed TNF normally at both the mRNA and protein levels as opposed to conventional LT alpha KO mice, which showed substantial decreases in TNF. Additionally, the spleens of the neo-free LT alpha KO mice displayed several features resembling those of LT beta KO mice rather than conventional LT alpha KO animals. The phenotype of the new LT alpha(Delta/Delta) mice indicates that LT alpha plays a smaller role in lymphoid organ maintenance than previously thought and has no direct role in the regulation of TNF expression.