Two populations of human blood basophils: effect of prednisone on circulating numbers

Phenotypic and Functional Heterogeneity of Low-Density and High-Density Human Lung Macrophages

BACKGROUND

Pulmonary macrophages are a highly heterogeneous cell population distributed in different lung compartments.

METHODS

We separated two subpopulations of macrophages from human lung parenchyma according to flotation over density gradients.

RESULTS

Two-thirds 65.4% of the lung macrophages have a density between 1.065 and 1.078 (high-density macrophages: HDMs), and the remaining one-third (34.6) had a density between 1.039 and 1.052 (low-density macrophages: LDMs). LDMs had a larger area (691 vs. 462 μm²) and cell perimeter (94 vs. 77 μm) compared to HDMs. A significantly higher percentage of HDMs expressed CD40, CD45, and CD86 compared to LDMs. In contrast, a higher percentage of LDMs expressed the activation markers CD63 and CD64. The release of TNF-α, IL-6, IL-10 and IL-12 induced by lipopolysaccharide (LPS) was significantly higher in HDMs than in LDMs.

CONCLUSION

The human lung contains two subpopulations of macrophages that differ in buoyancy, morphometric parameters, surface marker expression and response to LPS. These subpopulations of macrophages probably play distinct roles in lung inflammation and immune responses.

Systemic activation of basophils and eosinophils: markers and consequences

Basophils and eosinophils are important effector cells in human allergic diseases; they play a significant role in promoting allergic inflammation through the release of proinflammatory mediators (such as histamine, leukotriene C(4), major basic protein, eosinophil cationic protein, IL-4, and IL-13, among others). Notably, in allergic subjects, these cells exist in higher numbers and in a more activated state compared with nonatopic control subjects. Evidence for the greater activation state includes increased expression of intracellular and surface markers and hyperreleasability of allergy mediators. We have been interested in the phenotypic markers of effector-cell activation for many years. There is considerable overlap among activation markers, and few activation markers have been found that define a unique phenotype that is quantifiable in the assessment of the presence and severity of allergic disease. This review summarizes the existing evidence for systemic activation of human basophils and eosinophils in allergic diseases. The potential mechanisms responsible for functional and morphologic alterations in these effector cells and the specificity and utility of surface markers in the assessment of allergic disease activity or severity are also discussed.

Dexamethasone inhibits basophil migration

Glucocorticoids have been shown to inhibit the local accumulation of basophils during the allergen-induced late-phase reaction (LPR). Since migration is an essential step in the recruitment of basophils from the circulation, we examined whether the widely used glucocorticoid, dexamethasone (DEX), directly acts on basophils to inhibit the migration caused by C5a, interleukin (IL)-3, and IL-8. When purified basophils were preincubated with various concentrations of DEX, a dose-dependent inhibition was observed; DEX at concentrations as low as 1 nM reduced the number of migrated basophils by 30-40%; at higher concentrations, it showed a slightly stronger inhibitory effect. There was no significant difference in the effect of DEX on the migration caused by the three chemoattractants. The action of DEX took place rapidly; apparent inhibition was observed even when migration was initiated without preincubation. Although the inhibitory effect of this agent was not reversed when DEX was removed by washing, the inhibition was not mediated by the toxicity as measured by the trypan-blue exclusion test. These results indicate that the in vivo blocking effect of glucocorticoids on basophil accumulation during LPR is mediated in part by direct action to inhibit the migration of basophils.

Circulatory basophilia in guinea pigs with delayed-type hypersensitivity. Topical antigenic provocation induces circulatory basophilia

Circulatory basophilia could be induced in inbred guinea pigs systematically immunized with ovalbumin and consequently provoked repeatedly with dissolved ovalbumin applied onto the mucosa of the nares or the outer eye. The degree of the increase in circulatory basophil granulocytes depended on the adjuvant used and was significantly more pronounced after immunization with Freund's complete adjuvant than with alhydrogel (Al(OH)3). The degree of basophilia was also dependent on the animal strain, but different in two strains selected for high-asthma trait.

Pharmacokinetics and pharmacodynamics of methylprednisolone when administered at 8 am versus 4 pm

The temporal variations in the pharmacokinetics and pharmacodynamics of methylprednisolone at 8 AM versus 4 PM were investigated in six healthy male volunteers. Subjects completed three phases: no drug administration, 20 mg intravenous methylprednisolone at 8 AM, and the same dose at 4 PM. Methylprednisolone clearance was 28% greater in the afternoon. The suppressive effects of methylprednisolone on basophils (measured as whole blood histamine), helper T lymphocytes, and cortisol concentrations, assessed by the ratio of the area under the curve (AUC) after methylprednisolone to the baseline AUC, were not different between the phases. The 50% inhibitory concentration values for methylprednisolone derived from pharmacodynamic models were also similar, indicating no difference in intrinsic responsiveness. However, cortisol concentrations returned to baseline about 4 hours earlier after the 4 PM compared with the 8 AM dose because of the enhanced afternoon methylprednisolone clearance. These findings are in agreement with other studies that suggest adequate clinical effects and less disturbance of cortisol circadian behavior when methylprednisolone is administered as a single dose in the morning.

Two-compartment basophil cell trafficking model for methylprednisolone pharmacodynamics

A two-compartment closed model was used to characterize the movement of basophils between blood and extravascular sites resulting from methylprednisolone (MP) exposure. This model is consistent with the view that corticosteroids cause a decrease in the recirculation of these cells from peripheral compartments. Methylprednisolone (Solu-Medrol) was given to healthy males at doses of 10, 25, and 40 mg. Blood samples were collected and assayed for MP by HPLC for pharmacokinetic analysis. Whole blood histamine, an index of circulating basophils, was assessed by RIA over 32 hr. Nonlinear least-squares analysis was carried out to solve for the model parameters reflecting cell movement between compartments and sensitivity (IC50) to the steroid. This model quantitiates the fall and return pattern of biologic response to corticosteroids with a minimal number of parameters which jointly fit several dose/response curves and yields a mean IC50 value of 8.1 ng/ml similar to receptor binding of MP. Properties of the temporal and integrated response curve and model extrapolations over a wide dose range were explored with simulations. Because corticosteroids exert similar effects on other cells in blood, this model may be applicable to various regulatory and immunosuppressive effects.

Biological aspects of monocyte chemoattractant protein-1 (MCP-1)

In this communication, we have asked if MCP-1 is the mediator of cellular infiltration in DCH, outlining the criteria in Table 3. Preliminary data suggest that PHA-stimulated lymphocytes secrete MCP-1, and that MCP-1 can be produced in response to antigen stimulation. MCP-1 attracts monocytes and basophils, but not neutrophils. The question of a lymphocyte response to MCP-1 requires further study. We have emphasized that the discovery of leukocyte-specific NAP-1 and MCP-1 should now be followed by exploration of conditions in which one agonist is secreted without the other. This would be expected, for example, in DCH, which is characterized by mononuclear leukocyte infiltration without neutrophils.

Assessment of the systemic effects of inhaled glucocorticosteroids: the influence of blood sampling technique and frequency on plasma cortisol and leucocytes

Twelve healthy males (mean age 27.6 y, range 23-35 y) took part in a randomized, double-blind, cross-over study of the effect of blood sampling technique (separate isolated venepunctures vs use of an IV cannula) and frequency (overnight vs morning) on plasma cortisol and white blood cell count after inhalation of a single dose of budesonide 3.2 mg or placebo, in order to establish the more sensitive method for future use. Sampling technique and frequency affected neither leucocytes nor plasma or urinary cortisol. Budesonide suppressed both plasma and urine free cortisol and delayed the nocturnal rise due to the circadian rhythm, thus reducing the AUC of plasma cortisol vs time. Lymphocytes, eosinophils and monocytes were decreased and neutrophils and total white blood cells were increased by the high dose of budesonide used. Lymphocytes and neutrophils showed significant changes earlier than eosinophils and cortisol and may be the variables of choice under certain conditions. Frequent sampling gave more complete information about the systemic effect of the drug than single morning samples.

Steroid dose sparing: pharmacodynamic responses to single versus divided doses of methylprednisolone in man

Inhibitory drug interactions affecting the metabolism of methylprednisolone (MP) may produce either steroid sparing or adverse effects partly by increasing the exposure time to the steroid. This phenomenon can be mimicked by administering MP in divided doses. Two types of responses were compared after a single MP dose (40 mg bolus) and a divided regimen (20 mg bolus and a 5 mg bolus 8 hours later) in six healthy male volunteers. The suppression of basophils measured as whole blood histamine and plasma cortisol concentrations was assessed during 32 hours. The 37.5% reduction in dose produced a 23% overall decreased blood histamine response. A pharmacodynamic model for basophil cell distribution to and from an extravascular compartment describes the effects of MP after both regimens. A slower initial decline in blood histamine after the divided regimen may be related to incomplete suppression of basophil cell return to blood. The 50% inhibitory concentrations of MP of about 5 ng/ml were similar for both regimens. The decline and return of cortisol concentrations were similar between MP treatments with suppression continuing for 24 hours. The 50% inhibitory concentrations of MP values for adrenal suppression were about 1 ng/ml. Pharmacodynamic modeling is useful in quantitating corticosteroid responses and generally predicted the "dose-sparing" effects that were achieved by prolonging MP plasma concentrations. This study supports previous clinical observations that patients may require morning through evening exposure to MP to optimize efficacy while adrenal suppression is being minimized.

Pharmacokinetics and pharmacodynamic modeling of direct suppression effects of methylprednisolone on serum cortisol and blood histamine in human subjects

Pharmacodynamic models for "directly suppressive" effects of methylprednisolone are based on the premise that receptor interactions of steroids are followed by immediate suppression of either the circadian secretion of cortisol or the constant rate recirculation of histamine-containing basophils that persists until inhibitory concentrations of methylprednisolone disappear. Methylprednisolone doses of 0, 10, 20, and 40 mg were given as the 21-succinate sodium salt in a balanced crossover study to six normal men. Plasma steroid concentrations and blood histamine were measured simultaneously. Both forms of methylprednisolone exhibited linear kinetic parameters. One dynamic model quantitates the baseline circadian pattern and the decline and return of cortisol with similar parameter estimates for all three dose levels. A similar model describes the monoexponential decline and the log-linear return to steady-state baseline of blood histamine. Similar inhibitory concentration values for both effects approximated the equilibrium dissociation constant of in vitro steroid receptor binding. The new models are more physiologically appropriate for these steroid effects than three other models that are commonly employed in pharmacodynamics. Steroid effects generally appear to be receptor mediated with either nongene immediate responses or gene-mediated delayed effects. These models allow quantitation of the rapid effects of steroids with simple equations and common fitted parameters for all steroid dose levels.