Tyrisonase inhibition and melanin reduction of human melanocytes (HEMn-MP) using Anacardium occidentale L extract.

Cashew (Anacardium occindentale L) leaves extract (CLE) has potential as tyrosinase inhibitor that can be used for therapeutic in pigmentation problem. This study investigates the real potential of CLE to inhibit tyrosinase and melanin reduction using human epidermal melanocytes. The extracts were exposed to the human melanocytes for more than 24 hours. The CLE extract exhibited potential as tyrosinase inhibitor, reduced melanin and high in antioxidant activity relative to commercial extract of Emblica sp.

Tyrisonase inhibition and melanin reduction of human melanocytes (HEMn-MP) using Anacardium occidentale L extract

Cashew (Anacardium occindentale L) leaves extract (CLE) has potential as tyrosinase inhibitor that can be used for therapeutic in pigmentation problem. This study investigates the real potential of CLE to inhibit tyrosinase and melanin reduction using human epidermal melanocytes. The extracts were exposed to the human melanocytes for more than 24 hours. The CLE extract exhibited potential as tyrosinase inhibitor, reduced melanin and high in antioxidant activity relative to commercial extract of Emblica sp.

Activation of monocytic cells by monoclonal antibodies to the CD11a/18 (LFA-1) complex: mediation by Fc receptor.

IgG1 antibodies reacting with several monocytic antigens form a bridge between the specific antigen and the Fc receptors also expressed on these cells. This results in calcium mobilization and generation of superoxide. Single IgG1 antibodies reacting with the CD11a/CD18 cellular adhesion molecular complex do not, however, induce monocytic activation. This is not because they induce a negative signal, as the response to formyl-methionyl-leucyl2-phenylalanine (FMLP) or direct cross-linking of FcRII is not inhibited. Furthermore, a combination of an intact CD11a and CD18 antibody does induce a rise in intracellular calcium and production of superoxide. This activation is dependent on the binding of the Fc portion of both antibodies to Fc receptors, as F(ab')2 fragments do not cause activation. This suggests that simultaneous binding of opsonized bacteria to cellular adhesion molecules and to Fc receptors on monocytes would facilitate activation of these cells. Furthermore, it illustrates the importance of using F(ab')2 fragments in the analysis of signal transduction molecules on Fc receptor-bearing cells.

Binding of monoclonal antibody to CD16 causes calcium mobilization in large granular lymphocytes but inhibits NK killing.

A monoclonal antibody (mAb), CLB/FcR gran I, reactive with the CD16 Fc receptor (FcRlo/FcRIII) of human cells, leads to calcium mobilization in large granular lymphocytes (LGL) but not in granulocytes. Identical responses are obtained with F(ab')2 fragments of this antibody, indicating that the response is independent of Fc-FcR binding, and that bivalent cross-linking of this receptor is adequate for optimal calcium mobilization. The calcium response was greater in CD3- LGL compared to CD3+ LGL, although the response was augmented in the latter cells by prior rosetting with sheep red blood cells (SRBC). Calcium mobilization in CD3- LGL induced by CLB/FcR gran I is associated with inhibition of natural killer cell (NK) killing, and inhibition of the enhanced NK killing induced by the anti-CD2 low-density monoclonal antibody, 9.1. This supports the view that the NK-enhancing activity of 9.1 is due to simultaneous binding to CD2 and CD16, and may in fact be transduced through the CD16 molecule. The variable reported effects of anti-CD16 antibodies on NK killing are likely to reflect the epitope bound rather than the isotype of antibody used, since F(ab')2 fragments of CLB/FcR gran I also inhibit NK killing.

Mechanism of human monocyte activation via the 40-kDa Fc receptor for IgG.

It is shown that a mAb specific for the human 40-kDa FcR (FcRII) leads to activation of human monocytic cells but that extensive cross-linking of the receptor is required. Calcium mobilization can be induced in immature monocytic cells (undifferentiated U937 cells) and peripheral blood monocytes with an intact IgG1 anti-FcRII antibody (CIKM5) but not by F(ab')2 fragments of this antibody. The intact antibody can bind in a tripartite manner by its two F(ab') sites and its Fc-binding site whereas the F(ab')2 fragments of this antibody can only bind in a divalent fashion. A rise in intracellular free calcium ion concentration occurs when F(ab')2 fragments are cross-linked with F(ab')2 anti-mouse Ig indicating that more extensive cross-linking of FcRII is required rather than an obligatory requirement for an Fc-FcRII interaction. Calcium mobilization in response to intact or cross-linked F(ab')2 fragments of CIKM5 is associated with superoxide production only in IFN-gamma-primed peripheral blood monocytes and IFN-gamma differentiated U937 cells indicating that the activation signal produced via FcRII is inadequate to fully stimulate non-"primed" cells. A second mAb reactive with FcRII (2E1) does not cause calcium mobilization in monocytes or U937 cells, and partially blocks the effects of CIKM5. 2E1 also blocks CIKM5 superoxide production in IFN-gamma-primed monocytes and differentiated U937 cells. This may be explained in part by the fact that 2E1 is an IgG2a antibody and can only participate in bipartite binding with FcRII. When 2E1 is cross-linked with F(ab')2 anti-mouse Ig there is a small calcium response. This does not cause superoxide generation in IFN-primed monocytes but does do so in IFN-gamma differentiated U937 cells. FcRII is also expressed on granulocytes and some B cells but the effects of cross-linking the receptor on these cells differ from those seen in monocytes.

The effects of pertussis toxin on human T lymphocytes.

Purified pertussis toxin (PPT) is a potent mitogen for human T lymphocytes and is shown to cause rapid calcium mobilization in resting T cells, a T-cell line and CD3- lymphocytes with natural killer (NK) activity. In resting T cells the PPT activation is associated with cytoplasmic alkalinization. A similar rise in intracellular free calcium ([Ca2+]i) and cytoplasmic alkalinization is observed with activation through the antigen receptor complex. The effect of PPT is unlikely to be mediated through this pathway, however, as it can mobilize calcium in lymphocytes that do not express the CD3-Ti complex. In contrast to several other cell types, re-incubation of resting human T cells with PPT, up to a dose of 100 ng/ml for 2 hr does not block subsequent agonist-induced calcium mobilization dependent on G protein-mediated phospholipase C activation. Mitogenic doses of PPT cause a modest reduction in subsequent agonist responses, but this is likely to be due to a post-activation refractory state rather than G protein inactivation.

CD2 and CD3 antigens mobilize Ca2+ independently.

Antigen-induced stimulation of T cells is mediated via the CD3 antigen receptor (Ti) complex and monoclonal antibodies (mAb) reacting with CD3 and Ti result in rapid intracellular Ca2+ mobilization, followed by monocyte-dependent proliferation. Combinations of mAb to CD2, the sheep red blood cell receptor, also mobilize calcium and induce mitogenesis and purified phytohemagglutinin (PHA) stimulates T cells predominantly by interaction with this molecule. It has been suggested that activation via CD2 requires the presence of CD3 and that the hydrophobic epsilon chain of CD3 is the T cell calcium channel. To investigate this further we have obtained large numbers of natural killer (NK) cells which express CD2 but not CD3 from a patient with a chronic expansion of this lymphocyte subpopulation. It is shown that calcium mobilization can be induced in these cells by mAb to CD2 and purified PHA but not by anti-CD3 mAb. This indicates that calcium mobilization can be induced via the CD2 molecule in NK cells not expressing CD3 and that activation through CD2 is separate from the antigen receptor CD3 pathway.