Surfactant proteins, SP-A and SP-D, are collagen-containing calcium-dependent (C-type) lectins, called, collectins. Their primary structure has four regions: a cysteine-linked N- terminal region involved in multimerization, a collagen region composed of Gly-X-Y repeats, coiled-coil neck region, and the C-terminal carbohydrate recognition domains (CRD) or C-type lectin domain. SP-A looks like a bouquet, while SP-D is a cruciform- like structure, with four arms of equal length. SP-A and SP-D have been shown to act as innate immune molecules at pulmonary as well as extra-pulmonary sites by binding to pathogens, allergens and apoptotic/necrotic cells via their CRD region. SP-A and SP-D can induce pathogen neutralization and enhanced phagocytosis. In addition, SP-A and SP-D can interact via CRDs with allergens and dampen allergic reaction in vitro and in vivo. This thesis examines in vitro interaction of a recombinant fragment of human SP-D containing neck and CRD regions (rhSP-D) with IAV and Aspergillus fumigatus, in addition to characterizing a dichotomy of the effects of SP-A and SP-D on dendritic cells in an attempt to explain how SP-A and SP-D modulate DC functions differentially. Experiments involving interaction of rhSP-D with IAV pandemic strain show that it can be a restrictive factor against the virus, in addition to modulating immune response by a macrophage cell line. The rhSP-D can have anti-A. fumigatus effect directly and indirectly in the context of pathogen as well as allergen. A comparison has been made between two recombinant fragments of SP-D that have been expressed with and without 8 Gly-X-Y repeats for their fungistatic properties. The effects of SP-A and SP-D on cultured DC maturation, and effector cytokine and proliferative response of co-cultured cells have also been examined in vitro.

Aescin is a mixture of several acidic triterpenoid saponin glycosides found in the extracts of the horse chestnut tree. Horse chestnut, Aesculus Hipoocastanum, is one of the 25 domestic species of Aesculus that are mostly large, ornamental shade trees. Although known to be poisonous, the nuts of the horse chestnut are used by Amerindians, after detoxification. Horse chestnuts are said to have several traditional medicinal usages including even cancer. In this study the biochemical, genotoxic, and cytotoxic effects of aescin was studied using isolated lymphocytes, whole blood lymphocytes and HL-60 promyeloid leukemia cell lines. Cytotoxicity of aescin was examined by trypan blue viability staining of the cells in culture treated with varying aescin concentrations. It was observed that aescin was cytotoxic at all concentrations, for all cell types studied, except whole blood lymphocytes, where it was not cytotoxic at 10-9 and 10-10 M concentrations. Genotoxicity of aescin was examined by sister chromatid exchange and micronucleus. The genotoxic effect of Aescin was observed to be more significant over isolated lymphocytes compared to other cell lines. On the otherhand, aescin at 10-8 M and lower concentrations were observed to be non-genotoxic over whole blood lymphocytes whereas this concentration was considerably toxic for isolated lymphocytes and for HL-60 cell lines. Apoptotic properties of aescin were determined by DNA fragmentation, cytochrome c release and negative NAPO staining. All the Aescin concentrations tested resulted in apoptosis over HL-60 cell lines, whereas necrosis was not observed. However, isolated lymphocytes showed both apoptosis and necrosis upon treatment with 10-6 M to 10-8 M aescin, exhibiting apoptosis only at 10-9 M and 10-10 M. Biochemical effects of aescin were investigated by following GST and NAT enzyme activities. An increase in GST enzyme activity was observed over all cell lines treated with increasing aescin concentrations for 72 hours. Whereas NAT activity was decreased upon treatment with aescin in similar manner.