Wassim Y. Almawi

The prevalence of factor V R506Q mutation‐Leiden among apparently healthy Lebanese

Resistance to activated protein C (APC) degradation caused by a specific point mutation in the factor V (FV) gene, FV:R506Q or FV‐Leiden, which replaces Arg506 with Gln at the APC cleavage site within the FV gene, is the most prevalent inherited caused of venous thrombosis. Recent reports suggested that the prevalence of FV‐Leiden is high among Caucasians, and very low among non‐Caucasians, thereby suggesting that FV‐Leiden has originated as a single event in a primary focus. Insofar as FV‐Leiden is associated with increased risk of thromboembolic diseases, coupled with its selective worldwide distribution, the aim of this study was to determine the prevalence of FV‐Leiden in Lebanon and compare it with those of other countries of Caucasian and non‐Caucasian origin. FV‐Leiden was determined by PCR, followed by hybridization with specific wild‐type and mutant DNA probes. By screening 174 healthy Lebanese subjects, 25 were shown to carry the FV‐Leiden mutation, giving an allele frequency of 7.4% and an overall prevalence rate of 14.4%. Of the 25 FV‐Leiden carriers, 24 were in the heterozygous state while one was in the homozygous states. No statistical difference in the FV‐Leiden prevalence was noted with respect to age, gender, or sect. In addition to Lebanon, which had the highest prevalence rate reported thus far (14.4%), a high prevalence of FV‐Leiden was reported for Syria (13.6%), Greece–Cyprus (13.4%), and Jordan (12.3%), an indication that the Eastern Mediterranean is the primary focus of FV‐Leiden mutation. The high prevalence of FV‐Leiden in Lebanon suggests that screening for this mutation must be considered for those with a family history, and/or those with additional risk factors for venous thrombosis. Am. J. Hematol. 65:45–49, 2000.

Evidence that glucocorticosteroid-mediated immunosuppressive effects do not involve altering second messenger function

The mechanism by which glucocorticosteroids (GCS) suppress proliferation of human peripheral blood mononuclear leukocytes (PBML) was investigated. Using the proliferative responses to immobilized anti-CD3 mAb or mitogens (PHA+PMA) as biological readouts, dexamethasone (DEX) and 6α-methylprednisolone (6α-MP) were shown to inhibit PBML proliferation in a concentration-dependent fashion. The mechanism by which GCS mediate immunosuppression did not involve interference with Ca2+ fluxes as: (1) DEX failed to block Ca2+ entry into anti-CD3+PMA stimulated cells; and (2) Ca2+ ionophores (ionomycin and A23187) failed to circumfent DEX-mediated suppression. DEX also had no effect on protein kinase C (PKC) activity as: (1) inhibitors (H-7 and staurosporin) or stimulators (1,2-dihexanoyl-snglycerol [DiC6] and 1,2-dioctanoyl-rac-glycerol [DiC8]) of PKC did not prevent DEX-mediated suppression; (2) DEX did not affect the activation-induced upregulation of CD4 and CD8 expression, an indirect index of PKC activity; and (3) DEX did not alter the activation-associated translocation of PKC from cytosolic to membrane-bound compartments. This, in addition to previous results demonstrating that GCS directly inhibit cytokine gene transcription and that rII-1 + rIL-6 + rIFN-γ completely abrogated GCS-mediated suppressive effects, further supports the notion that GCS exert their immunosuppressive effects through inhibition of cytokine gene expression.

Suppression of pokeweed mitogen-driven human IgM and IgG responses by the hydroxylamine of sulfamethoxazole

OBJECTIVE To determine the effect(s) of reactive sulfonamide metabolites on antibody production by human lymphocytes. METHODS Human peripheral blood cells (PBMCs) were isolated from control volunteers and incubated with the hydroxylamine of sulfamethoxazole (SMX H/A), a reactive metabolite of the most commonly used sulfonamide, in increasing concentrations. PBMCs were then stimulated to produce antibody with pokeweed mitogen. After incubation for 8 days, concentrations of IgG and IgM were determined in supernatant using an ELISA assay. RESULTS Production of both IgG and IgM was significantly suppressed by sub-lethal concentrations of SMX H/A in a concentration-dependent fashion (p < 0.05). Suppression was more marked for IgM production (maximal decline to 80% of baseline antibody production) than for IgG production (maximal decline to 57% of baseline antibody production). No suppression was seen when cells were incubated with sulfamethoxazole in concentrations up to 400 microM. This suppression was not related to changes in cell viability; at a concentration of 25 microM of SMX H/A, IgM and IgG concentration were reduced by 47 +/- 8.7% and 73 +/- 7.2%, while cell viability (percentage of live cells) was 93 +/- 5%. Suppression was time-dependent, increasing over the incubation periods to reach a plateau after 2 h of incubation. CONCLUSION Sulfonamide reactive metabolites, in concentrations which are achieved during therapy, suppress antibody production by PWM-stimulated human cells. This may explain, in part, the alterations in immunity associated with hypersensitivity reactions to the sulfonamides. This may also have implications for patients receiving sulfonamide therapy and concurrent immunosuppressive therapy.

Posttranscriptional mechanisms of glucocorticoid antiproliferative effects: glucocorticoids inhibit IL-6-induced proliferation of B9 hybridoma cells.

Addition of rIL-6 to IL-6-dependent B9 cells starved for IL-6 for 16 – 20 h stimulated a vigorous proliferative response. Glucocorticoids (GCs), in a concentration-dependent manner, inhibited rIL-6-stimulated proliferation of B9 cells This inhibition was specific for the GCs, evident by the capacity of the GCs, dexamethasone, prednisolone, and hydrocortisone, but not non-GC steroids, to suppress rIL-6-dependent B9 cell proliferation. Furthermore, GC inhibition of IL-6-stimulated B9 cell proliferation was receptor mediated and was abrogated by the GC receptor antagonist, RU486. In addition to their reported effects on inhibition IL-6 expression, the results presented support the notion that GCs also acted distally by suppressing signal transduction through the IL-6 receptor.