Colloidal gold immunoultrastructural localization of rat surfactant

Ultrastructural study of nuclear inclusions immunohistochemically positive for surfactant protein A in pulmonary adenocarcinoma with special reference to their morphogenesis

To investigate the fine-structural nature of nuclear inclusions immunopositive for surfactant protein A (SP-A) antibody staining, a detailed ultrastructural study was performed, as well as immunohistochemical examination of pulmonary adenocarcinomas. Surgically resected tumor specimens from 31 patients were examined by immunohistochemistry focused on reactivity to SP-A and thyroid transcription factor 1 (TTF-1) antibodies. Only cases with >5% positive nuclear inclusions in cancer cells were considered positive, some of which were examined by electron microscopy. Immunohistochemically, 6 of 31 cases were doubly positive for SP-A and TTF-1 antibodies. On electron microscopy, SP-A-positive nuclei contained diffuse or globular fine granular substance as inclusions. Both types of globular and diffuse inclusions were sometimes connected to the inner nuclear membrane, in association with fragmented or stacked membranous structures. The findings of this study suggested that nuclear inclusions positive for SP-A antibody staining in adenocarcinomas of the lung were derived from accumulated content in the perinuclear cistern resembling pseudoinclusion processes and composed of proteins antigenically cross-reactive with SP-A.

Ca(2+)-dependent binding of annexin IV to surfactant protein A and lamellar bodies in alveolar type II cells

Surfactant protein A (SP-A), a lung-specific glycoprotein in pulmonary surfactant, is synthesized and secreted from the alveolar type II cells. It has been shown that SP-A is a Ca(2+)-binding protein with several binding sites and that the high-affinity site(s) is located in the C-terminal region of SP-A. In the present study we isolated the proteins from bovine lung soluble fraction that bind to SP-A in a Ca(2+)-dependent manner using DEAE-Sephacel and SP-A-conjugated Sepharose 4B. At least three different protein bands with molecular masses of 24.5, 32, and 33 kDa were observed on SDS/PAGE. The main protein, with molecular mass of 32 kDa, was identified as annexin IV by the partial-amino-acid-sequence analyses and an immunoblot analysis with anti-(annexin IV) antiserum. We also found from the immunoblot analysis that the cytosolic fraction of isolated rat alveolar type II cells contains annexin IV. In addition, when rat lung cytosol was loaded on to the lung lamellar body-conjugated Sepharose 4B in the presence of Ca2+, two proteins, with molecular masses of 32 and 60 kDa on SDS/PAGE respectively, were eluted with EGTA. The 32 kDa protein was shown to be annexin IV by an immunoblot analysis with the antiserum against annexin IV. The lung annexin IV augmented the Ca(2+)-induced aggregation of the lung lamellar bodies from rats. However, the augmentation of aggregation of the lung lamellar bodies by annexin IV was attenuated when the lamellar bodies were preincubated with polyclonal anti-SP-A antibodies. SP-A bound to annexin IV under conditions where contaminated lipid was removed. These results suggest that SP-A bound to annexin IV based on protein-protein interaction, though both proteins are phospholipid-binding proteins. All these findings suggest that the interaction between SP-A and annexin IV may have some role in alveolar type II cells.

An arthroconidial-spherule antigen of Coccidioides immitis: differential expression during in vitro fungal development and evidence for humoral response in humans after infection or vaccination

A 33-kDa protein antigen purified from spherules of Coccidioides immitis was analyzed for ultrastructural localization and for binding to serum antibodies from infected or immunized humans. By using colloidal gold detection of affinity-purified anti-33-kDa protein antibodies, electron photomicrographs showed binding to the inner cell wall of arthroconidia and spherules and to the septa and glycocalyx surrounding endospores. Enzyme immunoassay measurements also demonstrated that the antigen was most abundant in mature spherules. Of 37 patients with coccidioidomycosis but without concurrent human immunodeficiency virus infections, all but 2 demonstrated immunoglobulin M (IgM) (usually with early infection) or IgG antibodies for the 33-kDa antigen. In contrast, only one of four HIV-infected patients with active coccidioidal infections demonstrated antibody. On the other hand, 107 of 108 patients without evident coccidioidomycosis and 15 of 16 patients with histoplasmosis did not have similar antibodies, indicating a high degree of specificity. Immunization of humans with a spherule vaccine produced IgM responses to this antigen that were not evident in placebo recipients.

Vitamin K-dependent carboxylation of pulmonary surfactant-associated proteins

Rat type II pneumocytes expressed vitamin K-dependent carboxylase activity that incorporated 14CO2 into microsomal protein precursors of molecular weights similar to those of surfactant-associated proteins (SAP). Compared to carboxylated precursor proteins present in the liver, these molecules appeared to be unique to the lung. Antibodies raised against purified rat surfactant reacted with SAP resolved by NaDodSO4/PAGE and with surfactant-containing lamellar bodies in type II pneumocyte cytoplasm. NaDodSO4/PAGE of microsomal proteins, after carboxylase-catalyzed incorporation of 14CO2, demonstrated radiolabeled, immunoreactive products identical to SAP. The presence of gamma-carboxyglutamic acid in these proteins was confirmed by HPLC analysis of SAP hydrolysates. Furthermore, lung carboxylase activity and SAP matured over similar time courses during fetal lung development. These results show that SAP are carboxylated by type II cells via a vitamin K-dependent pathway analogous to that for hepatic carboxylation of clotting factors. Further analogy to the clotting system suggests that gamma-carboxyglutamic acid residues in SAP polypeptides play a role in Ca2+ binding and thus in the known requirements for both the cation and SAP in the physiological function of pulmonary surfactant.