Although SP-D is produced constitutively within the lung, protein accumulation and gene expression are inducible and increases in SP-D expression have been observed in a number of disease states or models (Tables 4 and 5 ). In general, the synthesis and secretion of SP-D increase in association with lung injury and activation of the respiratory epithelium [1] . For example, levels of SP-D mRNA and SP-D accumulation are increased within 24-72 h after intratracheal instillation of LPS [103 • ], and SP-D expression by alveolar and bronchiolar epithelial cells increases after exposure of rats to 95% O 2 for 12 h [104] . Keratinocyte growth factor (KGF) increases SP-D expression and protein production in association with pneumocyte hyperplasia and after injury caused by bleomycin [105] . In addition, the levels of SP-D can increase markedly in response to the overexpression of certain cytokines, such as interleukin-4, or in response to microbial challenge [91, 92] .