[Frontiers in Bioscience 1, e55-64, August 1,1996]
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CAVEAT LECTOR



IMMUNOGLOBULIN THERAPY IN KAWASAKI SYNDROME AND RSV PROPHYLAXIS

H. Cody Meissner, M.D.1, and Donald Y.M. Leung, M.D., Ph.D.2

1 Department of Pediatrics, Floating Hospital for Children at New England Medical Center; Tufts University School of Medicine, Boston, MA 02111;

2 Department of Pediatrics; The National Jewish Center for Immunology and Respiratory Medicine; Denver, CO 80262

3. Role of IVIG in Kawasaki Syndrome

KS is an acute vasculitis of infancy and early childhood first described by Tomasaku Kawasaki in 1967 (7). This vasculitis can involve all small and medium arteries throughout the body but particularly targets the coronary arteries (8). The clinical features associated with KS are listed in Table I (9). Features of this disease are similar to those found in certain diseases which are recognized to be caused by toxin-producing bacteria, such as toxic shock syndrome and scarlet fever. Untreated KS is generally a self-limited illness lasting 2 to 3 weeks. Coronary artery involvement occurs in 20 to 25% of patients who do not receive therapy within 10 days following the onset of fever (10). Studies in Japan and the United States demonstrated that IVIG plus aspirin given within the first 10 days of onset of fever reduce the prevalence of coronary artery abnormalities to less than 5% (11, 12). Early studies evaluated IVIG at a dose of 400 mg/kg given on 4 consecutive days (10). A subsequent multicentered study demonstrated that a single dose of IVIG, 2 gm/kg, with aspirin was more protective against formation of coronary artery aneurysms (12). In addition to reducing coronary artery disease, high dose IVIG therapy results in a more rapid normalization of laboratory values (albumin, -antitrypsin, C-reactive protein) as well as more rapid resolution of clinical symptoms (12).

Table I. Diagnostic Features of Kawasaki Syndrome

1. Fever

2. Non exudative, bilateral conjunctivitis

3. Changes in the oral cavity, including:

strawberry tongue
erythematous
fissured lips
hyperemic pharynx

4. Changes in the peripheral extremities:

induration and erythema of hands and feet
periungual desquamation
5. Polymorphous rash

6. Cervical lymphadenopathy

(at least one node > 1.5cm diameter)

It was also noted that a lower peak IgG level was associated with a worse clinical outcome, suggesting that a therapeutic threshold was necessary to achieve benefit (12). The duration of fever and the degree of inflammation as measured by laboratory tests such as the erythrocyte sedimentation rate was inversely related to the peak IgG level. Even more importantly, the peak serum IgG level following IVIG therapy was significantly lower in those children who developed coronary artery disease. A recent meta-analysis evaluated the efficacy of aspirin and IVIG in the prevention of coronary artery abnormalities (13). The authors concluded that, while both high-dose and low-dose aspirin therapy were associated with a similar risk of coronary artery disease, IVIG at a dose of >1.0 gm/kg was associated with a lower risk of coronary artery involvement than lower doses of IVIG. During a 3 day observation, a single high dose IVIG of 2 gm/kg resulted in a lower incidence of coronary artery disease than when multiple doses of 400 mg/kg IVIG were received. These data suggest that a specific serum IgG concentration must be achieved before inflammation is arrested.

The mechanism(s) accounting for the efficacy of IVIG in the treatment of KS is unknown. However, it is widely agreed that this illness has an infectious etiology. This observation is based on both epidemiologic and clinical findings. In Japan as well as the United States there is an endemic incidence of disease on which epidemics and even pandemics may be superimposed (14). One well documented outbreak in Japan which occurred between November 1985 and May 1986, started around Tokyo, extended to North and South and ultimately involved most of Japan (15). This epidemiologic pattern of spread strongly suggests that the disease is due to an infectious microorganism that may be readily transmitted among young children. Seasonal peaks of KS tend to occur in late winter and spring (14). The peak incidence of KS occurs between 12 and 24 months of age, with over 80% of cases occurring before 5 years of age (14). This disease rarely occurs in adolescents or in children less than 6 months of age. This age distribution is typical of other infectious diseases such as paralytic polio in the pre-vaccine era and varicella in unvaccinated children. It is possible that early in the first year of life, children lose protective maternal antibody, and gradually acquire an immunity during childhood so that by adolescence the disease becomes uncommon.

Extensive serologic and microbiologic studies have failed to identify a consistent microbial agent associated with cases of KS (14). However, studies of the immune response in patients with KS reveal an unusual degree of stimulation (16, 17). The acute stage of KS is associated with increased numbers of activated helper T cells and reduced numbers of suppressor T cells (18-20). A marked polyclonal B cell activation present during the acute phase is reduced by treatment with IVIG (18, 19). Cytokine levels including levels of IL-1, TNF-alpha, IFN-gamma and IL-6 are elevated during the acute phase of the disease and return to normal during convalescence (21-26). Circulating antibodies that appear during the acute stage are cytotoxic to cytokine-stimulated vascular endothelial cells (27, 28). Furthermore, tissue from a fatal case of KS demonstrated endothelial cell activation with the expression of cytokine-inducible molecules such as HLA-DR antigens (29). A mononuclear cell infiltrate consisting of activated CD4 and CD8 T cells as well as monocytes was also seen.

IVIG therapy results in a reduction of the acute symptoms as well as normalization of many of the immunologic aberrations seen in acute KS. Specifically, aspirin and IVIG therapy is associated with an increase in the number of circulating CD8+ T cells, a reduction in the number of activated helper T cells and a reduction in the number of B cells. Several theories have been proposed to explain these immunologic effects by IVIG (Table II). It is likely that IVIG modifies the inflammatory response through more than one mechanism. For example, several reports suggest that IVIG production acts directly on cytokine gene expression via transcriptional and post-transcriptional modulation (30). This suggests that IVIG may downregulate the immune response by a nonspecific immuno-modulatory mechanism. In addition, IVIG may neutralize a causative toxin that results in the massive immune stimulation associated with KS (6).

Table II. Possible Mechanisms of IVIG Action in Kawasaki Syndrome

1. Anti-idotypic modulation of anti-endothelial anti-bodies.

2. Inhibition of cytokine-induced endothelial acti-vation.

3. Reduction of cytokine production.

4. Anti-toxin specific antibodies which neutralize the causative superantigen.


Staphylococcal enterotoxins and strepto-coccal pyrogenic exotoxins (SPE) B and C have the ability to activate B cells, T cells and macrophages (reviewed in references 31 and 32). These bacterial products have been defined as superantigens. Such toxins bind to the class II MHC proteins on the surface of the antigen presenting cells and stimulate T cells which express particular Vß gene segments. Similarly, superantigens are potent stimulators of IL-1 and TNF-alpha production by macrophages (33). Patients with toxic shock syndrome, a prototypic example of disease caused by a superantigen (TSST-1), have a dramatic expansion of Vß2+ T cells (34).

To determine whether the immune activation associated with acute KS represents a response to superantigen(s), studies were conducted on the T cell repertoire of patients in the acute phase of KS (35, 36). Peripheral blood mononuclear cells from 19 patients with acute KS were analyzed for T cell receptor Vß gene expression using two methods: semiquantitative polymerase chain reaction analysis and flow cytometry. Patients with KS demonstrated elevated levels of Vß2 and Vß8.1 T cells in comparison to cells from control patients with other febrile illnesses which showed no changes (35). During convalescence, the proportion of Vß2 and Vß8.1 T cells returned to normal levels. Other Vß T cell populations were analyzed and comparisons were made between acute and convalescent specimens of patients with KS from Japan as well as two sites in the United States. None of the other Vß populations were found to be elevated. These results are consistent with the hypothesis that the immune stimulation of KS is triggered by a bacterial toxin with superantigenic activity. This selective expansion of circulating Vß2 T cells is similar to the changes in peripheral blood lymphocytes described in toxic shock syndrome, an illness that shares many clinical manifestations of KS (35). Such a marked expansion of T cells expressing a specific Vß rarely occurs in response to a conventional antigen. A second study using a Vß2 specific monoclonal antibody confirmed the increased expression of Vß2 and to a lesser degree of Vß8.1 in peripheral blood T cells of 13 patients with acute KS (36).

Following our report in 1992, several other groups examined the TCR repertoire during the acute stage of KS. A report by Pietra et al.. did not detect an increase in any particular Vß family (37). However, one patient with acute KS demonstrated elevated Vß2 T cells and two patients demonstrated a decrease in Vß2 T cells. During convalescence, these changes reverted to normal consistent with a superantigen effect in these patients. In this regard, superantigens are capable of causing either elevations or reductions in circulating T cells bearing specific TCR Vß's. A report by Sakaguchi et al. also failed to detect expansion of CD4 and T cells bearing Vß2 or Vß8 receptors among Japanese children with acute KS (38). The authors suggested that superantigens initiating the immunopathology of KS in various geographic locations may be different (38).

An alternative explanation is that the ability to detect expansion of Vß-specific T cells is dependent on the time interval after onset of illness. Indeed a recent study by Curtis et al. (39) did confirm increased Vß2+ T cells in acute disease. However, significantly elevated percentages of Vß2+ T cells were detected only during the second week of illness. During the first week and after the second week of acute KS, T cells did not demonstrate Vß skewing. After the second week of illness, stimulated T cells may have already migrated to tissues and therefore may no longer be detectable in the peripheral blood. Therefore, the reason that some investigators have had difficulty in demonstrating T cell abnormalities may be attributed to the timing of collections of the blood specimen.

In a recent report by Leung et al., myocardial tissue and coronary artery tissue were studied from a patient who died of acute KS (40). Immunohistochemical examination of the mono-nuclear cell infiltrate of frozen tissue sections from the myocardium and the right coronary artery as compared to spleen demonstrated enhanced Vß2 expression in the coronary artery, particularly in the myocardium. Sequence analysis of the Vß2 chain genes from T cells isolated from the myocardium demonstrated extensive junctional region diversity. While the response to stimulation by most conventional antigens results in cells with limited junctional diversity of the T cell receptor, extensive junctional diversity is a typical response to a superantigen.

In a separate study, Yamashiro and his colleagues reported a selective expansion of Vß2+ T cells in the small intestinal mucosa of patients with acute KS but not in the control subjects (41). Based on these observations, they suggested that the GI tract may be the primary site of entry for a superantigen-secreting organism causing acute KS. Indeed, preliminary data from their group also indicates that staphylococci and streptococci can be isolated from small intestinal fluid of KS patients.

Considering that three independent groups of investigators have found evidence of increased numbers of Vß2+ T cells in acute KS, the next important hurdle was identification of the putative superantigen(s). To determine the potential superantigen(s) involved in this Vß2+ T cell expansion, Leung et al. carried out the following study (41): Samples from sixteen consecutive patients with KS were cultured for the presence of superantigen producing gram-positive bacteria. Skin (groin, axilla) and mucous membrane (rectum, throat) cultures were obtained from 16 patients who satisfied established criteria for KS before IVIG therapy was administered. Fifteen control patients with fever and rash served as control. All group A ß hemolytic streptococci and all coagulase positive S. aureus isolates were screened for toxin production. Cultures from patients with KS and control patients were screened in blinded fashion. Bacteria producing superantigens were found in 13 of 16 KS patients, but they were present in only 1 of 15 control patients (p<.0001). Eleven of 13 toxin positive cultures from patients with KS were due to TSST elaborating S. aureus and 2 of 13 were due to streptococci producing SPEB and SPEC. TSST-1 and SPEC are known to possess superantigenic activity which stimulate expansion of Vß2+ T cells.

Twelve of the 13 culture positive patients had toxin producing S. aureus isolated from the mucous membranes of the upper or lower gastrointestinal tract. Only 1 of 13 patients had toxin producing bacteria on the skin and none showed bacteria colonizing the mucous membranes. This is consistent with the observation of Yamashiro et al. (41) of marked Vß2+ T cell expansion in the gastrointestinal tract of patients with acute KS.

Since this report in 1993, TSST secreting S. aureus have been isolated from a number of patients with KS from different regions of the United States. These include KS patients with coronary artery disease (Schlievert and Leung, unpublished observations). However, one group has been unsuccessful at detecting this organism from patients with KS (43). The inability to recover this organism may be due to the relatively low concentration of this toxin producing Staphylococcus on the surface of mucous membranes. To reliably identify toxin producing strains, we have found it necessary to meticulously study numerous colonies from each culture. The failure to find seroconversion to TSST-1 has been used as evidence against a role for this toxin in KS (43). However, this approach is flawed because seroconversion rarely ever occurs following the acute phase of other superantigen-mediated diseases such as staphylococcal TSS. Furthermore, all such KS patients were treated with high dose IVIG which is known to inhibit antibody synthesis.

Takei et al. (6) has demonstrated that IVIG contains high concentrations of neutralizing antibodies which inhibit the T cell response to eight different staphylococcal superantigens. Using affinity absorption techniques, it was shown that this T cell inhibitory effect was mediated by anti-toxin specific antibodies in IVIG. Clinical and subclinical infections with S. aureus presumably result in production of antibodies to staphylococcal toxins with increasing age. Pooled IVIG which is obtained from several thousand donors can be expected to contain variable titers of antibodies to staphylococcal toxins. Thus, it is possible that the beneficial effect of IVIG in KS is, in large part, due to the presence of antibody which inhibits bacterial toxin-induced stimulation of the immune response.

As noted earlier, there appears to be a threshold IgG level which is necessary to reduce the prevalence of coronary artery disease in patients with KS. In fact, certain patients require more than one dose of IVIG before demonstrating a beneficial effect (44). In an earlier report, we demonstrated considerable variation between four different IVIG preparations in their ability to inhibit superantigenic activity due to TSST-1 (45). We propose that certain patients who fail to satisfactorily respond to IVIG may not have attained a sufficient titer of antibodies to bacterial toxins. In these situations, sequential doses may be necessary to achieve a protective titer. We have also provided evidence that children who develop KS lack immunity to TSST-1 at the time of presentation, while convalescent specimens contain passively acquired activity against TSST-1 derived from IVIG therapy (45). We believe that acquisition of this activity is responsible for the resolution of symptoms.

In Figure I, a possible sequence of events in the pathogenesis of KS is proposed: a susceptible host becomes colonized on the mucous membranes by a superantigen-producing organism, most often a coagulase-positive S. aureus, although other toxin producing bacteria may be involved. In a host who lacks antibodies to toxin, the toxin is absorbed resulting in selective stimulation of Vß2+ T cells. A cascade of immune stimulation follows, with an increase in the number of activated helper T cells, B cells and macrophage/monocytes. Macrophage stimulation results in an elevated levels of cytokines. The elevated cytokine levels induces fever and the clinical findings of KS as well as the increased levels of acute phase reactants. Increased cytokine levels also results in the expression of new antigens on the surface of endothelial cells, making the cells susceptible to cytotoxic antibodies, more throm-bogenic and more susceptible to attack by leukocytes. Selective infiltration of Vß2 T cells into the coronary arteries and the myocardium leads to vascular injury and myocarditis and results in formation of aneurysms. The unusually severe irritability in patients with KS may be a direct neurotoxic effect of the bacterial toxin.

Figure I: Postulated scenario for pathogenesis of Kawasaki Syndrome.

It should be noted, however, that the lack of anti-toxin antibodies as a risk factor for superantigen-mediated diseases has only been shown for Toxic Shock Syndrome. Indeed, in patients with atopic dermatitis, who are chronically colonized with high numbers of superantigen producing staphylococci, we have found high serum IgG titers to staphylococcal toxins. Nevertheless, application of toxins or superantigens to their skin results in an inflammatory skin lesion indicating that circulating anti-toxins do not prevent onset of local inflammation in response to superantigens. Thus, aside from toxin neutralization, the administration of IVIG in acute KS is likely to have a number of different immunomodulatory effects that leads to reduced inflammation.

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