infection. On admission, she had fever and a white count of 28,000. Because of the fascial necrosis, the infection had spread rapidly within subcutaneous planes through her face and down her neck. There also had been extension into the retrobulbar orbit.

Treatment of this disease includes high-dose intravenous antibiotics. In this case, we used clindamycin and cefotaxime. Our objective, however, was to restore the normal physiology as soon as possible. The patient’s immunosuppression could not be immediately reversed and, given the fulminant course, was a longer-term goal. At that moment, the intravascular thrombosis was causing ischemic necrosis, which provided additional substrate for the bacteria. To break that cycle, this patient was treated with hyperbaric oxygen (nine sessions of 90 min at 2.4 atm).

In addition, she was treated with serial debridement of necrotic tissue. A temporary tarsorrhaphy was placed because of the anticipated cicatricial changes.

With this treatment, the area of facial involvement contracted, and after about 2 weeks, a bed of sterile granulation tissue could be grafted. Six months later, eyelid function was normal and vision remained 20=20.

In summary, our successes and our challenges in the area of orbital infection relate to the ongoing dynamic between microbe and host. Bacterial infections will never be eliminated because they are caused by our normal flora, which simply gain the upper hand when our defenses are down. However, we can minimize the inflicted damage by promptly recognizing how, and to what degree, the normal physiology has been altered, and by taking measures that discourage bacterial growth and strengthen host defenses.

And don’t forget the antibiotics.

ACKNOWLEDGEMENTS

Supported in part by core grant EY01931 from the National Eye Institute, Bethesda, Maryland, and by an unrestricted grant from Research to Prevent Blindness, Inc., New York U.S.A.

REFERENCES

1.Harris GJ. Subperiosteal abscess of the orbit. Arch Ophthalmol 1983; 101:751–757.

2.Harris GJ. Subperiosteal inflammation of the orbit: a bacteriological analysis of 17 cases. Arch Ophthalmol 1988; 106: 947–952.

3.Harris GJ. Subperiosteal abscess of the orbit: age as a factor in the bacteriology and response to treatment. Ophthalmology 1994; 101:585–595.

4.Harris GJ, Bair RL. Anaerobic isolates from a subperiosteal abscess in a 4-year-old patient. Arch Ophthalmol 1996; 114:98.

5.Harris GJ. Subperiosteal abscess of the orbit: computed tomography and the clinical course. Ophthal Plast Reconstr Surg 1996; 12:1–8.

6.Garcia GH, Harris GJ. Criteria for nonsurgical management of subperiosteal abscess of the orbit: analysis of outcomes 1988–1998. Ophthalmology 2000; 107:1454–1458.

7.Harris GJ. Subperiosteal abscess of the orbit: older children and adults require aggressive treatment Editorial. Ophthal Plast Reconstr Surg 2001; 173:395–397.

8.Bisno AL, Stevens DL. Streptococcal infections of the skin and soft tissues. N Engl J Med 1996; 334:240–255.

9.Feingold DS. Group A streptococcal infections: an old adversary reemerging with new tricks? Arch Dermatol 1996; 132:67–70.

10.Kronish JW, McLeish WM. Eyelid necrosis and periorbital necrotizing fasciitis: report of a case and review of the literature. Ophthalmology 1991; 98:92–98.

began to dissect the mechanisms of inflammation including identification of protein regulators of that control the cellular responses.

Inflammation is a multifactoral response to an injury and is comprised of innate and adaptive responses. The innate response to a pathogen=toxin is an antigen nonspecific process that is mediated largely by macrophages, neutrophils, natural killer (NK) cells, and complement. Adaptive responses to a pathogen=toxin are antigen specific responses. Activation of T- and B-cells by antigen presenting cells is required for acquired immunity, so the time course of this response is delayed in comparison to the innate response. The acquired immune response can be further divided into the humoral and cellular responses. Humoral responses are antibody driven and the down-stream effectors include complement activation and antibody-driven phagocytosis. Cellular responses are mediated largely by T-cells and include both T helper cell (Th) 1 and Th2 responses. The majority of this discussion will focus on the cellular responses in inflammation.

The contribution of inflammation to disease can be both beneficial and detrimental. Inflammation is a process that normally protects the host from injury and, as such, attenuation of this response can lead to increased susceptibility to infection. On the other hand, certain diseases are a result of dysregulated inflammation and in these instances inflammation may be viewed as detrimental. In these circumstances, down-regulation of specific aspects of the inflammatory response may be beneficial. Indeed, animal studies have shown that inhibition of certain immune functions can attenuate the development of atherosclerosis (1). Also, depletion of negative regulators of the immune response can increase the severity of atherosclerosis (2). Thus, determination of the specific mechanisms through which inflammation contributes to a disease process is necessary, and understanding the general mechanisms of the inflammatory response may aid in understanding specific events. Further, since one of the main mechanisms in the pathogenesis of many inflammatory disorders involves the effects of

inflammation on the vasculature, specific focus will be given in this discussion to those components that affect vascular structure and function.

Once an inflammatory response is triggered, activated leukocytes must localize to the injured area in order to carry out their effector functions. This process requires leukocyte extravasation from the blood into the tissue, migration to the site of injury, and subsequent further activation. Leukocyte extravasation is generally believed to occur by distinct steps that consist of loose rolling, tight adhesion, and diapedesis. Each step is mediated by the interactions of particular molecules on the cell surface of leukocytes and endothelial cells (EC) . Although the exact mediators of these interactions differ slightly between types of leukocytes, the adhesive and migratory events are generally believed to be mediated in the following way. The initial interaction between leukocytes and endothelial cell (EC) is mediated by selectins on leukocytes and carbohydrate moieties (Sialyl-LewisX) on the surface of the endothelium. This loose binding slows the leukocyte to allow the stronger integrin–selectin interactions to proceed. Subsequent strong binding of leukocytes with cell adhesion molecules on the endothelial surface results in flattening and stopping of the rolling leukocytes, which then diapedeses through the endothelium (3). New reports have suggested that the molecular binding interactions between leukocytes and EC may also initiate signal transduction pathways that serve to provide outside-in signals to EC (4). Future work in determining the targets and cellular effects of these signal transduction pathways on endothelial biology will be helpful in further understanding the intricate leukocyte–endothelial interactions that occur during this process.

One of the main cellular mediators of the inflammatory response is the macrophage, which under steady-state conditions accumulates in tissues and serves two main functions. They phagocytose pathogens and toxins, and are also very important ‘‘professional’’ antigen presenting cells necessary for the activation of the adaptive immune response. After initiation of an inflammatory response,

macrophages can aid in the clearance of pathogens=toxins by both antibody-dependent and independent mechanisms. Further, several recent reports have suggested that macrophages can contribute to the cytotoxic immune response by inducing apoptosis of target cells through a FasL-dependent mechanism (5,6).

Adaptive immunity is mediated by T-cell responses to pathogens or allogeneic tissue. The T-cell response can be loosely divided into those mediated by T helper cells (Th) and cytotoxic T-cells (CTL) . The Th response can be further divided into the Th1 and Th2 response, the balance of which is governed by the relative amounts of interleukin (IL)-4 and interferon-lambda (IFNg) available. Recognition of foreign antigens by the T-cell receptor results in different cytokine profiles secreted by Th2 and Th1 cells. Th2 cells secrete many cytokines including IL-4, 5, and 6. These cytokines can activate B-cells and mobilize the humoral response. Th1 cells secrete IFN? and IL-2, leading to the activation of the cytotoxic immune response that is mediated largely by CTL (7). Recognition of foreign antigens by CTL results in the secretion of interferons (IFN) and activation of death inducing pathways. The IFN response protects target cells from viral infection by reducing proliferation and gene expression in these cells. Interferons can also induce apoptosis of some cell types. Activated T-cells also induce apoptosis of virus infected or foreign cells through FasL and granzyme=perforinmediated pathways. FasL is a death inducing ligand that can activate caspases through the formation of death signaling complexes at the plasma membrane (8). Granzymes are a family of serine proteases that activate apoptosis through several mechanisms that include direct caspase activation, release of mitochondrial factors, and direct cleavage of cellular components (9).

Negative regulators of the inflammatory response, including IL-10 and transforming growth factor-beta (TGF- b), are important in ensuring the inflammatory response does not become pathologically dysregulated. IL-10 is secreted by macrophages and Th2 cells in a temporally delayed fashion as compared to proinflammatory cytokines. The majority of

IL-10 actions in vivo may depend on its ability to block nuclear factor kappaB (NF-kB) and mitogen-activated protein kinase (MAPK) activation, which in turn results in decreased proinflammatory cytokine secretion, EC–leukocyte interactions, antigen presentation, and Th1 activation (10,11). The importance of these regulatory actions can be observed in IL-10 knockout mice, which, although possessing an increased resistance to pathogenic infection, have an overall detrimental pathological enhancement of their inflammatory response to these infections (12–14). Transforming growth factor-b is a pleiotropic growth factor that is expressed as a latency-associated peptide (LAP) . Cleavage of LAP is required for the biological activity of TGF-b. This growth factor can inhibit several aspects of inflammation, including proinflammatory cytokine secretion, cell adhesion molecule expression, and inducible nitric oxide synthase (iNOS) and activation. Further, TGF-b can also affect vascular structure and function by inhibiting smooth muscle proliferation and normalizing vasodilation (15). Insight into the importance of TGF-b in regulating the inflammatory response is supplied by knockout models of TGF-b in which the mice die in utero due to excessive inflammation (16). Further, inhibition of TGF-b activity utilizing neutralizing antibodies promotes plaque destabilization in mouse models of atherosclerosis, implicating TGF-b in the pathogenesis of some inflammatory disorders (17).

Many biochemical mediators regulate the cellular components of the inflammatory response. Because of the impact of nitric oxide (NO) and eicosanoids on vascular structure, we will focus on the contribution of these factors to inflammation. Nitric oxide is a potent vasodilator that is synthesized by a constitutively expressed endothelial NO synthase (eNOS) and an inducible form of NO synthase (iNOS) . Low levels of NO, like those formed by eNOS, are normally secreted by the endothelium and negatively regulate inflammatory responses by inhibiting leukocyte adhesion, migration, and activation. However, in response to several stimuli and under many pathological conditions, increased expression and activation of iNOS results in the release of large amounts of

from the tissue. The increased release of inflammatory factors such as tumor necrosis factor-alpha (TNF-a), IL-1, vascular endothelial growth factor (VEGF), iNOS, and eicosanoids can either directly or indirectly enhance vascular permeability by altering endothelial cell structure or expression of adhesion molecules. For instance, the systemic release of large

Figure 1 (Facing page) Regulatory mechanisms in inflammation. Release of cytokines such as tumor necrosis factor-alpha (TNF-a) and interleukin (IL)-1b, and large amounts of nitric oxide (NO) by tissue macrophages activates the endothelium. Expression of carbohydrate moieties, selectins, and cell adhesion molecules (CAM) by this monolayer recruits leukocytes to the site of injury by facilitating leukocyte transmigration. This process of loose-rolling, tight adhesion, and diapedesis is followed by leukocyte chemotaxis toward the site of injury. Once activated, macrophages can elicit effector functions that include antibody-dependent and -indepen- dent phagocytosis, and induction of receptor-mediated apoptosis of some cells. Recognition of foreign antigen in areas of inflammation by T-cells can initiate either a T helper cell (Th)1 or Th2 response. The Th2 response activates B-cells, resulting in mobilization of the humoral response. The Th1 response can initiate a cytotoxic T-cell response towards cells expressing foreign antigen, leading to T-cell mediated apoptosis of target cells that is regulated primarily through FasL and granzyme=perforin pathways. Nitric oxide and eicosanoids can regulate inflammatory responses as well as affect vascular structure and function. When synthesized at low levels, NO can inhibit leukocyte transmigration and activation. However, when NO is synthesized at high levels, it can activate leukocytes, and induce vasodilation. Depending on the type of receptor expressed on effector cells, eicosanoids can either activate or inhibit leukocyte activation and transmigration. These lipid signal transduction mediators can also increase vasodilation. Negative regulators, such as IL-10 and transforming growth factor-beta (TGF-b), are important in reducing the inflammatory response once an infection has been cleared. IL-10 and TGF-b can both inhibit cytokine expression and secretion, cell adhesion molecule expression, antigen presentation, and activation of the Th1 response. Additionally, TGF-b can inhibit inducible nitric oxide synthase (iNOS) expression and activation, and can normalize vasodilation.

amounts of TNF-a during septic shock dramatically increases endothelial permeability, leading to damage of the surrounding tissue and eventual organ failure (21,22). The overall effect of this increased permeability may be observed as the fundamental characteristics of inflammation originally observed by the Romans.

Because one of the key requirements for a sustained and effective response to wound healing is the delivery of nutrients and cellular components to the site of injury, increased angiogenesis is an important event in many inflammatory responses. There are likely several angiogenic mediators that control the process at different stages of the inflammatory response. During the initial stage of a response to an injury, secretion of basic fibroblast growth factor (bFGF) has been suggested to induce the growth of new blood vessels. However, since bFGF is mainly expressed during the early stages of the healing process, other factors are likely involved in angiogenesis. During the later stages of wound healing, VEGF is expressed in high concentrations and may promote angiogenesis. VEGF is a very potent angiogenic factor that is secreted by macrophages and EC (23). Further, recent reports have suggested that CD40L, a T-cell activator and important regulator of immune responses, may also increase angiogenesis, potentially by up-regulating the secretion of VEGF from the endothelium (24).

Since several ocular and orbital conditions are a result of a dysregulated inflammatory response, appreciation of the processes is increasingly important to understanding the pathogenesis of these conditions. An example is the impact of inflammation on vascular structure and growth, since the neovascularization of several components of the eye is responsible for decreasing vision in conditions, such as age-related macular degeneration and diabetic retinopathy. Effective treatments, such as photodynamic therapy, are currently available to treat ocular neovascularization (25). However, understanding the inflammatory processes that contribute to ocular neovascularization may be important in the development of therapeutic regimens that are less injurious and more permanent in their effects.

REFERENCES

1.Laurat E, Poirier B, Tupin E, Caligiuri G, Hansson GK, Bariety J, Nicoletti A. In vivo downregulation of T helper cell 1 immune responses reduces atherogenesis in apolipoprotein E-knockout mice. Circulation 2001; 104:197–202.

2.Mallat Z, Besnard S, Duriez M, Deleuze V, Emmanuel F, Bureau MF, Soubrier F, Esposito B, Duez H, Fievet C, Staels B, Duverger N, Scherman D, Tedgui A. Protective role of interleukin-10 in atherosclerosis. Circ Res 1999; 85:el7–e24.

3.Delves PJ, Roitt IM. The immune system. First of two parts. N Engl J Med 2000; 343:37–49.

4.Hu Y, Szente B, Kiely JM, Gimbrone MA Jr. Molecular events in transmembrane signaling via E-selectin. SHP2 association, adaptor protein complex formation and ERK1=2 activation. J Biol Chem 2001; 276:48549–48553.

5.Boyle JJ, Bowyer DE, Weissberg PL, Bennett MR. Human blood-derived macrophages induce apoptosis in human plaque-derived vascular smooth muscle cells by Fas-ligand= Fas interactions. Arterioscler Thromb Vasc Biol 2001; 21: 1402–1407.

6.Seshiah PN, Kereiakes DJ, Vasudevan SS, Lopes N, Su BY, Flavahan NA, Goldschmidt-Clermont PJ. Activated monocytes induce smooth muscle cell death: role of macrophage colonystimulating factor and cell contact. Circulation 2002; 105: 174–180.

7.Delves PJ, Roitt IM. The immune system. Second of two parts. N Engl J Med 2000; 343:108–117.

8.Granville DJ, Carthy CM, Hunt DW, McManus BM. Apoptosis: molecular aspects of cell death and disease. Lab Invest 1998; 78:893–913.

9.Bleackley RC, Heibein JA. Enzymatic control of apoptosis. Nat Prod Rep 2001; 18:431–440.

10.Schottelius AJ, Mayo MW, Saartor RB, Baldwin AS. Interleukin10 signaling blocks inhibitor of kappaB kinase activity and nuclear factor kappaB DNA binding. J Biol Chem 1999; 274: 31868–31874.

11.Suttles J, Milhom DM, Miller RW, Poe JC, Wahl JC, Stout RD. CD40 signaling of monocyte inflammatory cytokine synthesis through an ERK1=2-dependent pathway. A target of interleukin (il)-4 and il-10 anti-inflammatory action. J Biol Chem 1999; 274:5835–5842.

12.Kane MM, Mosser DM. The role of IL-10 in promoting disease progression in leishmaniasis. J Immunol 2001; 166: 1141–1147.

13.Murray PJ, Young RA. Increased antimycobacterial immunity in interleukin-10-deficient mice. Infect Immun 1999; 67: 3087–3095.

14.Deckert M, Soltek G, Geginat S, Lutjen M, Montesinos-Rongen H, Hof H, Schluter D. Endogenous interleukin-10 is required for prevention of a hyperinflammatory intracerebral immune response in Listeria monocytogenes meningoencephalitis. Infect Immun 2001; 69:4561–4571.

15.Tedui A, Mallat Z. Anti-inflammatory mechanisms in the vascular wall. Circ Res 2001; 88:877–887.

16.Shull MM, Ormsby I, Kier AB, Pawlowski S, Diebold RJ, Yin M, Allen R, Sidman C, Proetzel G, Calvin D, Annunziata N, Doetschman T. Targeted disruption of the mouse transforming growth factor-beta 1 gene results in multifocal inflammatory disease. Nature 1992; 359:693–699.

17.Mallat Z, Gojova A, Marchiol-Fournigault C, Esposito B, Kamate C, Merval R, Fradelizi D, Tedgui A. Inhibition of transforming growth factor-beta signaling accelerates atherosclerosis and induces an unstable plaque phenotype in mice. Circ Res 2001; 89:930–934.

18.Abramson SB, Amin AR, Clancy RM, Attur M. The role of nitric oxide in tissue destruction. Best Pract Res Clin Rheumatol 2001; 15:831–845.

19.Funk CD. Prostaglandins and leukotrienes: advances in eicosanoid biology. Science 2001; 294:1871–1875.

20.Tilley SL, Coffinan TM, Koller BH. Mixed messages: modulation of inflammation and immune responses by prostaglandins and thromboxanes. J Clin Invest 2001; 108:15–23.

21.Penn MS, Saidel GM, Chisolm GM. Vascular injury by endotoxin: changes in macromolecular transport parameters in rat aortas in vivo. Am J Physiol 1992; 262:H1563–H1571.

22.Dormehl IC, Hugo N, Pretorius JP, Redelinghuys IF. In vivo assessment of regional microvascular albumin leakage during coli septic shock in the baboon model. Circ Shock 1992; 38: 9–13.

23.Lingen MW. Role of leukocytes and endothelial cells in the development of angiogenesis in inflammation and wound healing. Arch Pathol Lab Med 2001; 125:67–71.

24.Melter M, Reinders ME, Sho M, Pal S, Geehan C, Denton MD, Mukhopadhyay D, Briscoe DM. Ligation of CD40 induces the expression of vascular endothelial growth factor by endothelial cells and monocytes and promotes angiogenesis in vivo. Blood 2000; 96:3801–3808.

25.Granville DJ, McManus BM, Hunt DW. Photodynamic therapy: shedding light on the biochemical pathways regulating porphyrin-mediated cell death. Histol Histopathol 2001; 16:309–317.