Particular ultrastructural aspects of human Paneth's cells]

Our research is about the ultrastructural aspects of Paneth cells obtained from human jejunal mucosa. The cells appear columnar in shape and show a roundish nucleus; their cytoplasm is characterized by a great amount of R.E.R. and by typical large granules in sopranuclear position. Our results confirm those previously described by other authors about the morphology of Paneth cells. In our specimens we have found moreover a variable number of particular cytoplasmic structures; these may show a fibrillar or granular matrix and are always surrounded by a membrane.     

Staphylococcus aureus-induced suppression of contact sensitivity in mice: suppressor cells elicited by polyclonal B-cell activation are regulated by idiotype--anti-idiotype interactions

Staphylococcus aureus strain Cowan I, a strong polyclonal B-cell activator (PBA), inhibited contact sensitivity to oxazolone in mice when administered 24 hr before sensitization. This suppression was mediated by idiotype-positive (Id+) B lymphocytes, which arose very early during the sensitization process and induced anti-Id B cells. These cells were found at Day 3 of the sensitization process and exerted their effect by activating antigen-specific suppressor T lymphocytes, which affected the efferent phase of the immune response. S. aureus strain Wood 46, which lacks of the ability to act as a PBA, was unable to inhibit contact sensitivity. These results indicate that PBA may play an important role in the regulation of cell-mediated immune reactions.     

Host preferences of the cocoa pod borer,Conopomorpha cramerella,the main threat to cocoa production in Southeast Asia

Insects ensure the survival of their offspring by depositing their eggs in suitable environments. Even generalist egg-laying insects often show preferences for specific host plants. The cocoa pod borer (CPB), Conopomorpha cramerella (Snellen) (Lepidoptera: Gracillariidae), successfully infests and reproduces on relatively few host plants, but has a major economic impact only on cocoa, Theobroma cacao L. (Malvaceae). Choice tests were performed in the laboratory to compare the frequency of insect visits, the duration of the visits, and the number of eggs laid on the fruits for each combination of host plants tested – that is, cocoa clones or fruits of rambutan (Nephelium lappaceum L.), Fijian longan (Pometia pinnata JR Forst & G Forst, both Sapindaceae), and langsat (Lansium domesticum Corrêa, Malvaceae). Our laboratory study showed that, when given the choice, CPB significantly favored cocoa pods over other host fruits (rambutan, langsat, or Fijian longan). Females also deposited more eggs on unripe fruits than on ripe fruits of similar size. The preference to lay eggs on specific cocoa clones in the bioassays did not reflect the level of the clone resistance to CPB damage reported from the field. Consequently, oviposition preference of female CPB does not seem to be the main factor explaining field resistance of some cocoa clones to CPB infestation.     

Growth of the androgen-dependent tumor of the prostate: Role of androgens and of locally expressed growth modulatory factors

The crucial role played by androgens in the growth of prostatic carcinoma is now well established. However, the mechanisms of this proliferative action are still poorly understood. Experiments have been performed to clarify: (1) the metabolism of androgens in prostatic tumor cells; and (2) the role played by locally produced growth factors in the autocrine regulation of prostatic tumor cell proliferation and the possible regulation exerted by testosterone (T) on the activity of these factors. These studies have been performed by utilizing the human androgen-responsive prostatic cancer LNCaP cell line. (1) By incubating LNCaP cells with different ¹⁴C-labeled androgenic precursors, it has been shown that all the major key enzymes involved in the metabolism of androgens (5-reductase, 17β-hydroxysteroid-oxidoreductase, 3- and 3β-hydroxysteroid-oxidoreductases) are present and active in these cells. In particular, the 5-reductase, which converts T and Δ₄ to DHT and 5-A respectively, seems to be more active when Δ₄ is the substrate, suggesting a preference for this precursor. (2) The hypothesis that LNCaP cells might produce LHRH (or a LHRH-like peptide) has been verified by RT-PCR, performed in the presence of a pair of specific oligonucleotide primers. A cDNA band of the expected size (228 bp), which specifically hybridized with a ³²P-labeled LHRH oligonucleotide probe, has been obtained in LNCaP cells. To clarify the possible role played by this factor in the regulation of tumor growth, LNCaP cells, cultured in steroid-free conditions, have been treated with a LHRH antagonist; the treatment resulted in a significant increase of cell proliferation. Taken together, these data indicate that a LHRH (or LHRH-like) growth modulatory system is expressed in LNCaP cells and plays an inhibitory role in the regulation of tumor cell proliferation. This system seems to be regulated in a negative way by steroids. Growth factors endowed with stimulatory activity, such as EGF and TGF, have also been shown to be produced by LNCaP cells. The present studies show that the immunoprecipitation of the EGF receptor with a specific monoclonal antibody (Ab225) reveals a protein band of the expected size (170 kDa) which is phosphorylated even in basal conditions. Moreover, the treatment of LNCaP cells, cultured in serum-free conditions, either with a monoclonal antibody against the EGF receptor, or with immunoneutralizing antibodies against EGF and TGF, results in a significant decrease of cell proliferation. These observations clearly confirm the expression, in prostatic tumor cells, of an EGF/TGF loop which exerts a stimulatory action on cell proliferation. T seems to exert a positive regulation on this loop, at least in terms of EGF receptor concentration.     

Study of permeation and blocker binding in TMEM16A calcium-activated chloride channels

We studied the effects of mutations of positively charged amino acid residues in the pore of X. tropicalis TMEM16A calcium-activated chloride channels: K613E, K628E, K630E; R646E and R761E. The activation and deactivation kinetics were not affected, and only K613E showed a lower current density. K628E and R761E affect anion selectivity without affecting Na⁺ permeation, whereas K613E, R646E and the double mutant K613E + R646E affect anion selectivity and permeability to Na⁺. Furthermore, altered blockade by the chloride channel blockers anthracene-9-carboxylic acid (A-9-C), 4, 4''-Diisothiocyano-2,2''-stilbenedisulfonic acid (DIDS) and T16inh-A01 was observed. These results suggest the existence of 2 binding sites for anions within the pore at electrical distances of 0.3 and 0.5. These sites are also relevant for anion permeation and blockade.