The effect of UV-B irradiation on primary and secondary HSV-1 infections in interleukin-4 knockout mice

Abstract Ultraviolet B (UV-B) irradiation suppresses cell-mediated immunity and may lead to increased susceptibility to infectious diseases. Limited evidence suggests that exposure promotes a T helper (Th) 2 type of cytokine response with abrogation of a Th1 response. Several putative mediators of UV-induced immunosuppression have been identified, of which interleukin-4 (IL-4), an example of a Th2 cytokine, is one. Primary and secondary epidermal infections with herpes simplex virus (HSV) type 1 in IL-4 knockout (IL-4^–/–) mice and the parent strain Bb 129 strain (IL-4^+/+) were investigated using clinical features, phenotyping of cells from lymph nodes draining the sites of infection and lymphoproliferation assays. The IL-4^–/– mice were more susceptible to both primary and secondary HSV infections than the parent mice. The percentage of lymph node dendritic cells (DC) expressing Ia was 45 in the IL-4^+/+ mice but only 18 in the IL-4^–/– strain, and the lymph node cells from infected IL-4^–/– mice were less able to respond in vitro to HSV than those from the parent strain. Following suberythemal UV-B irradiation, more severe primary and secondary lesions resulted in both strains. There were fewer lymph node DC expressing Ia in both strains and this change was accompanied by suppression of the lymphoproliferation induced by HSV which was due to an effect on DC function rather than on the proliferative ability of the responding lymphocytes. UV-B exposure had no effect on ICAM-1 or B7.2 expression on the DC. Thus IL-4 seems to protect mice against HSV infection, and no evidence was obtained for the involvement of IL-4 in the UV-induced immunomodulation which results in more severe cutaneous HSV infections. Received: 14 January 1999 / Received after revision: 23 March 1999 / Accepted: 26 March 1999     

Topical phosphonoacetic acid treatment of cutaneous herpes simplex infections in the guinea pig

Phosphonoacetic acid (PAA) was evaluated as therapy for primary cutaneous herpes simplex virus (HSV) infections in guinea pigs. Epilated areas of skin were inoculated with HSV type 1 and treated in a blind fashion with topical PAA 2% cream or placebo cream, the initial application varying from 3 to 84 hours after inoculation. PAA applied 3 hours after inoculation aborts clinical infection. Even when applied 84 hours after inoculation (12 hours after the appearance of clinical lesions), PAA reduces the severity of primary HSV infection, and thus may be suitable for the treatment of human HSV infections.     

Detection of multinucleated giant cells in differentiated keratinocytes with herpes simplex virus and varicella zoster virus infections by modified Tzanck smear method

Herpes simplex virus (HSV) and varicella zoster virus (VZV) infections induce the formation of intraepidermal vesicles containing acantholytic cells and multinucleated giant cells in the skin. The Tzanck smear is most commonly used to diagnose cutaneous herpetic infections, but it leads to many false‐positive and ‐negative results. This study aimed at establishing a method detecting much larger multinucleated giant cells using the Tzanck smear because these cells characterize the viral cytopathic effect in skin infections. Morphological changes were analyzed among several layers of keratinocytes with HSV‐ or VZV‐related cutaneous lesions, clinically and in vitro. We compared the sensitivity of the Tzanck smear to detect large acantholytic cells using both the removed roof tissue part (our approach) and the floor of the lesion (conventional approach) of a fresh vesicle. Large acantholytic cells were detected 2.0‐times more frequently in the removed roof tissue part of the vesicle than in the floor of the lesion. Round cells were much larger in the removed roof tissue part of the vesicle corresponding to the granular or prickle layer of the epidermis than in its floor of the lesion corresponding to the basal or prickle layer with the Tzanck smear. Differentiated cultured keratinocytes formed multinucleated giant cells by cell‐to‐cell fusion with resolution of cell membrane with VZV infection. Differentiated keratinocytes promote multinucleated giant cell formation by cell‐to‐cell fusion with HSV‐1 or VZV infection. To increase the sensitivity, the Tzanck smear should be prepared from the removed roof tissue part of a fresh vesicle to detect multinucleated giant cells in herpetic infections.     

Effects of ultraviolet radiation on the pathogenesis of Mycobacterium lepraemurium infection in mice

The purpose of this study was to determine whether exposing mice to ultraviolet radiation (UVR) would alter the pathogenesis of infection with Mycobacterium lepraemurium (MLM), which causes a chronic, progressive, lethal disease in susceptible mouse strains. BALB/c mice were irradiated on dorsal skin with various doses of UVR from FS40 sunlamps 3 days before infection with MLM in the hind footpad. The course of disease was followed by assessing the number of acid-fast bacteria in the footpad, regional lymph node and spleen, and measuring the size of the lesion at the site of MLM infection at various times after infection. Mice were also tested periodically for a delayed-type hypersensitivity (DTH) response by injecting MLM antigen into the uninfected footpad and measuring footpad swelling 24 hours later. Mice treated with a single high dose of UVR (45 kJ/m2) had significantly more bacteria in the infected footpad, lymph node and spleen than unirradiated control animals. They also had larger lesions at the site of MLM infection and exhibited significant suppression of the DTH response at 3 and 6 months after infection. Injection of mice s.c. in the footpad with MLM 3d after 45 kJ/m2 UVR reduced the median survival time from 391 to 305 d and after i.v. infection from 171 to 139 d. Dose-response studies indicated that exposing mice to 2.3 kJ/m2 of UVR, which is approximately 1 minimal erythemal dose for this strain, suppressed the DTH response by 50% at 3 months after infection.(ABSTRACT TRUNCATED AT 250 WORDS)     

Characteristics of cutaneous cytomegalovirus infection in non-acquired immune deficiency syndrome, immunocompromised patients

BACKGROUND: Although cytomegalovirus (CMV) disease is a severe complication among immunocompromised patients, its cutaneous features have not been frequently reported. As herpes simple virus (HSV) infection commonly develops in CMV skin lesions, a study is needed on the pathogenetic role of CMV in cutaneous lesion formation. OBJECTIVES: The purpose of this study is to characterize the clinical and histopathological features of cutaneous CMV infection and to determine whether CMV plays a true pathogenetic role in cutaneous lesions, or if it is just an innocent bystander during HSV infection among non-AIDS (acquired immune deficiency syndrome), immunocompromised patients. PATIENTS AND METHODS: A total of nine human immunodeficiency virus-negative patients diagnosed with cutaneous CMV infection from July 1999 to February 2005 at Samsung Medical Center were analysed in terms of their clinical and histopathological characteristics. In addition, we examined for the co-presence of HSV by performing immunohistochemical analysis and polymerase chain reaction. RESULTS: All the patients were immunocompromised; five had haematological diseases and four were organ transplant recipients. The clinical and histopathological features were similar to those of previous studies of patients with AIDS. Multiple anogenital ulcerations were the most frequent cutaneous presentation (66.7%). Most cytopathic changes were found in the dermis, particularly within the vascular endothelial cells (77.8%) and macrophages (66.7%). However, the association of CMV with concurrent HSV infection was even lower than that seen in patients with AIDS. Only one patient revealed a co-existing cutaneous HSV infection. CONCLUSIONS: In non-AIDS individuals, the cutaneous lesions from CMV infection showed similar clinical and histopathological features to those of patients with AIDS. However, skin lesions may not be highly associated with HSV, and CMV does seem to contribute to lesion development as a cutaneous manifestation among the CMV infected, non-AIDS, immunocompromised patients.     

Characteristics of dermal invasion in experimental cutaneous candidiasis of leucopenic mice

The course of experimental cutaneous Candida albicans infections produced in mice made leucopenic by the administration of cyclophosphamide was compared to that in untreated animals. In the latter, neutrophils characteristically infiltrated the area of infection and the organisms were virtually always confined to the epidermis. However, even though many fewer foci of infection were associated with neutrophils in the cyclophosphamide-treated animals, a majority of these foci were also unable to penetrate past the epidermis. Although Candida yeast proliferated relatively poorly when cultured in homogenates of skin lacking the epidermis, Candida pseudohyphae could invade into the dermis if inoculated skin was isolated from normal animals and cultured in vitro, or if the epidermis was removed by gentle scraping prior to inoculation with Candida yeast onto the remaining skin of leucopenic animals. Therefore, in the absence of neutrophil contact and killing of Candida pseudohyphae in the epidermis, other cutaneous defense mechanisms appear to be capable of preventing invasion of a majority of the organisms into the dermis. These findings may help to explain why deep Candida infections are rare in patients who have extensive superficial candidiasis.     

Development of an in vitro keratinocyte model for use in the study of HSV specific cytotoxicity

Herpes simplex virus (HSV) specific immune mediated cytotoxicity may be involved in control of HSV infections and in the tissue damage induced by HSV infection or HSV related skin disease such as herpes associated erythema multiforme. Developing an in vitro model to study this process has proved difficult due to the lack of an appropriate target cell that will express HSV antigens but is not simultaneously subject to viral induced cell death. The purpose of this study was to develop a model in which keratinocytes express cell surface HSV specific antigens but at the same time are protected from death due to viral infection. We found that keratinocytes infected with HSV in the presence of acyclovir (ACV) expressed such antigens yet remained viable for a period of time after the onset of antigen expression such that cytotoxicity studies could be successfully performed. Rabbit skin cells, a transformed keratinocyte line, or second passage human neonatal foreskin keratinocytes were grown in culture medium with or without 200 microM ACV and were infected with HSV. Examination by direct immunofluorescence with anti-HSV antibody revealed uniform HSV antigen expression by cells both with and without ACV by 8 h after infection. Cells infected without ACV exhibited marked structural abnormalities including formation of multinucleated giant cells, while cells with ACV showed fewer such changes throughout a 24-h period. An Ethidium Bromide-Acridine Orange cytotoxicity assay demonstrated significant increases in the cytotoxicity of infected cells not protected by ACV compared to that of cells with ACV (p less than .001). This in vitro model should prove useful in the investigation of HSV specific immune mediated cytotoxicity.     

Peculiar vegetative tumor-like genital herpes simplex nodules with brisk tissue eosinophilia in patients with human immunodeficiency virus infection

Genital herpes simplex virus (HSV) infection in a human immunodeficiency virus (HIV) patient can present as a vegetative nodule. Clinical differential diagnoses of the nodule include condyloma latum, condyloma acuminatum, viral or fungal infection, and cutaneous neoplasms. Histological examination of herpetic nodules has been reported to show thick pseudoepitheliomatous hyperplasia with dense dermal lymphoplasmacytic infiltrate and multifocal multinucleated cells with herpetic viral cytopathic changes. We report two patients with HIV presenting with vegetative tumor-like HSV nodules with distinctive histopathologic pattern of inflammation that has not been described in the literature before. All samples displayed slightly acanthotic epidermis with focal ulceration, dense dermal sclerosis, scattered plasma cells, and a brisk lymphoeosinophilic infiltrate found dissecting between dense collagen bundles. This pattern of inflammation is an important clue that can guide the pathologist to look for focal herpetic viral changes in the epidermis, as patients with HIV possibly tend to amount a predominantly eosinophilic immune response in inflammatory skin conditions.     

Growth of herpes simplex type 1 on skin explants of atopic eczema

In a novel approach to looking at why some children with atopic eczema are susceptible to cutaneous herpes simplex virus (HSV) infections, this study evaluates the hypothesis that HSV replicates more easily on eczematous than normal skin. Growth of HSV on eczematous skin explants was compared wild growth on explants from three control groups (psoriasis, Darier's disease and normal skin) over a 2-day period. Growth of HSV was significantly less on normal skin than in atopic eczema, psoriasis and Darier's disease. Virus replicated more quickly, and grew to higher titre within 24h, in eczematous and psoriatic explants than in normal skin. A defect in skin barrier function and host defence factors including local cytokine secretion are discussed as possible mechanisms in causing the increased susceptibility of children with atopic eczema to HSV infection.     

Interleukin‐33 is expressed in the lesional epidermis in herpes virus infection but not in verruca vulgaris

Interleukin (IL)‐33 is released on cell injury and activates the immune reaction. IL‐33 is involved in antiviral reaction in herpes virus infection, but the source that secretes IL‐33 has not been identified. We speculate that keratinocytes injured in herpes virus infection secrete IL‐33. In order to detect IL‐33 in the lesional epidermis of patients with herpes virus infection, we immunostained several cutaneous herpes virus infection samples with an anti‐IL‐33 antibody, and compared them with cutaneous human papilloma virus (HPV) infection samples. We observed strong nuclear and mild cytoplasmic staining in epidermal keratinocytes of the lesional skin samples with herpes simplex virus and varicella zoster virus infections. However, staining was not observed in the epidermis of verruca vulgaris (VV) samples. We assumed that the strong immune reaction to herpes virus infection may depend on strong IL‐33 expression in the epidermis, while very weak immune reaction in samples from patients with VV may be due to low or no expression of IL‐33 in the lesional epidermis.     

Acyclovir bioavailability in human skin.

Clinical experience demonstrates that oral acyclovir (ACV) is superior to topical ACV in treating recurrent cutaneous herpes simplex virus type 1 (HSV-1) infections. Cutaneous HSV-1 infections are complex in their pathology, affecting the basal epidermis in skin as well as establishing a latency phase in sensory ganglia. In vitro and in vivo human skin model systems were used in the present study to quantitate ACV disposition and absorption in skin and blood following two routes of administration and to investigate whether bioavailability differences were the result of insufficient drug delivery. Physiochemical and physiologic parameters determined from these experiments were used to develop a mathematical model to predict ACV disposition and absorption in human subjects. Model predictions and in vivo data agree; topical administration of commercial 5% ACV ointment and cream result in a 48 times greater total epidermal ACV concentration than after oral administration. Mathematical modeling of the ACV concentration gradient through the epidermis revealed, however, that the drug concentration in the target site of HSV-1 infections, the basal epidermis, is 2-3 times less after topical administration than after oral administration. Thus, the observed lack of clinical efficacy with topical ACV therapy in the recurring HSV-1 infection likely reflects the insufficient delivery of the drug to the target site of the HSV-1 infection, the basal epidermis.     

Syringitis: A clue to herpes infection

Herpes simplex virus (HSV) is a member of the herpes virus family that commonly affects the skin. Typical histopathologic findings are usually limited to the epidermis and include intraepidermal vesicles or ulceration and epidermal necrosis. More specific findings in herpes virus infection include enlarged and pale keratinocytes, with steel-gray nuclei and margination of chromatin at the edge of the nucleus and ballooning degeneration. Although histopathologic changes may occasionally involve the hair follicles or sebaceous glands, it is very rare to find HSV involving the eccrine glands. We present a case of a 13-month-old child with a large body burn diagnosed with HSV (in the absence of the epidermis) by the presence of syringitis with herpetic features in the absence of the epidermis to aid in diagnosis.     

Infection with influenza a virus leads to flu antigen-induced cutaneous anaphylaxis in mice

It is well established, that viral infections may trigger urticaria or allergic asthma; however, as viral infections induce T helper 1 polarized responses, which lead to the inhibition of T helper 2 cell development, the opposite would be plausible. We wanted to investigate how viral infections may mediate allergic symptoms in a mouse model; therefore, we infected BALB/C mice with influenza A virus intranasally. Histologic analyses of lung sections and bronchoalveolar lavages were performed. In addition, cells from the mediastinal lymph nodes were restimulated in vitro to analyze which types of cytokines were induced by the flu infection. Furthermore, flu-specific antibody titers were determined and local anaphylaxis was measured after rechallenge with flu antigen. We found that airways inflammation consisted predominately of macrophages and lymphocytes, whereas only a few eosinophils were observed. interferon-gamma but no interleukin-4 and little interleukin-5 could be detected in the culture supernatants from in vitro restimulated T cells from the draining lymph nodes. The antibody response was characterized by high levels of virus-specific IgG2a, IgG2b, and IgG1 and, surprisingly, low levels of virus-specific IgE antibodies. Interestingly, flu-infected mice developed active and passive cutaneous anaphylaxis after rechallenge with flu-antigen. As the passive cutaneous anaphylaxis reaction persisted over 48 h and was significantly lower after passive transfer of the serum, which was IgE depleted, local anaphylaxis seemed to be mediated predominately by specific IgE antibodies. Taken together, our results demonstrate that mice infected with flu virus develop virus-specific mast cell degranulation in the skin. Our results may also have implications for the pathogenesis of urticaria or other atopic disorders in humans.     

Immunological Studies of herpes simplex virus infection in children with atopic eczema

Summary This study examines the role of immune defence mechanisms in herpes simplex virus (HSV) infections in atopic eczema and whether impairment of these mechanisms explains the susceptibility of some children with atopic eczema to cutaneous HSV infections. Ten children with eczema herpeticum and 13 with atopic eczema and recurrent HSV infection affecting multiple skin sites were studied, together with relevant control groups. In all children with atopic eczema, in vitro lymphoproliferation in response to stimulation with concanavalin A (Con A) was significantly decreased and natural killer (NK) cells (CD16 + 56) were reduced compared with non-atopic controls. IL-2 receptors, a marker for lymphocyte activation, were decreased during the acute phase of eczema herpeticum, and for 1 month thereafter. A positive stimulation index (>3) to HSV antigen, and high HSV lgG antibody titres measured by ELISA. Western blotting and neutralization assay, were seen in children with eczema herpeticum by 6 weeks, and also in children with atopic eczema and recurrent HSV infections. No evidence of an HSV-specific immune defect (either cell-mediated or humoral) was found in atopic eczema. Impairment of cell-mediated immunity in atopic eczema and recurrent HSV infections. No evidence of an HSV-specific immune defect (either cell-mediated or humoral) was found in atopic eczema. Imairment of cell-mediated immunity in atopic eczema was suggested by the reduced response to Con A. It is likely that reduced numbers of circulating NK cells and a decrease in IL-2 receptors during early eczema herpeticum contribute to the susceptibility of children with atopic eczema to cutaneous HSV infections.     

An erythematous maculopapular eruption in macaques infected with an HTLV-III-like virus (STLV-III)

A cutaneous maculopapular eruption has been previously described in humans infected with HTLV-III/LAV, the etiologic agent of acquired immunodeficiency syndrome. In this study, rhesus monkeys were prospectively examined after infection with an HTLV-III-like virus (STLV-III) to ascertain the incidence and clinical course of gross and histologic alterations of the skin. Between 1-3 weeks after inoculation, 83% of infected animals developed a transient cutaneous maculopapular eruption of the face, groin, and trunk. Histologically, the affected skin was characterized by a superficial perivascular infiltrate of mononuclear cells with associated endothelial cell hypertrophy and degeneration. This eruption preceded opportunistic infections, neoplasms, and other overt clinical signs commonly associated with an immunodeficiency syndrome. The findings suggest that STLV-III infection in the rhesus monkey closely simulates that which occurs in HTLV-III-infected individuals, and that the skin may represent a site of altered immunoregulation early in the course of this disease.     

Detection of herpes simplex virus DNA in cutaneous lesions of erythema multiforme

The association between erythema multiforme (EM) and herpes simplex virus (HSV) infection has long been appreciated, although the exact role which HSV may play in the pathogenesis of this herpes-associated EM (HAEM), is unknown. Previous studies have suggested, but not definitively demonstrated, the presence of HSV in lesions of HAEM. The presence of HSV would support the hypothesis that an immune-mediated response directed against HSV-specific antigens in the skin is central to lesion development in HAEM. The purpose of this study was to examine lesions of EM for the presence of HSV DNA by using the polymerase chain reaction (PCR). In addition, in situ hybridization using an HSV-specific RNA probe was performed to further localize the HSV nucleic acids within the skin. DNA was extracted from formalin-fixed, paraffin-embedded specimens of cutaneous lesions of HAEM and also from EM for which no precipitating factor could be documented, otherwise known as idiopathic EM (IPEM). DNA from lesions of bullous pemphigoid served as a negative control. Using PCR to specifically amplify HSV sequences which might be present, and then performing Southern analysis, we demonstrated HSV DNA in 9/13 HAEM and 6/9 IPEM biopsies. No HSV was detected in six lesions of bullous pemphigoid. In situ hybridization of three cutaneous HAEM lesions using an 35S-labeled HSV-specific RNA probe localized the HSV nucleic acids predominantly to the epidermis. Three biopsies of chronic dermatitis, used as negative controls, did not demonstrate this specific hybridization. These findings confirm the presence of HSV in lesions of HAEM and are consistent with the concept of an HSV-specific immune-mediated pathogenesis for this disease. In addition, most cases of IPEM appear to be herpes associated despite the absence of clinically apparent HSV infection.     

Update on antiviral therapy for herpes simplex virus infection

ABSTRACT: The prevalence of infection with herpes simplex virus (HSV) continues to increase largely due to the inability of current antiviral agents to eradicate latent infection. This article reviews strategies to slow the transmission of HSV infection, most importantly through the development of vaccines, as well as established and emerging choices for treatment of primary and recurrent genital herpes, herpes labialis, infections in immunocompromised hosts, and acyclovir-resistant infections. The role of chronic suppressive therapy in the management of genital herpes as well as its potential impact on transmission rates will also be discussed.
Herpes simplex virus (HSV) is a widespread pathogen in the United States, with more than 100 million U.S. citizens having serologic evidence of HSV-1 infection and 40–60 million, nearly one-fifth of the adolescent and adult population, infected with HSV-2 (1,2) . The prevalence of HSV-2, the major cause of genital herpes, has increased 30% since the late 1970s (2) . The fact that most of those infected with HSV are asymptomatic and yet may still be subclinically shedding virus further complicates efforts to slow the spread of transmission (3) . Therefore proper management of herpetic infections requires that the clinician be able to effectively diagnose those with HSV infection, to educate them regarding means of spread and symptoms indicative of infection, and to adequately treat infections which are identified in order to alleviate patient symptoms and slow the transmission of the virus. We review options for preventing infection, treating primary infections, and treating recurrent infections in order to accomplish these goals.     

Identification and characterization of 20 immunocompetent patients with simultaneous varicella zoster and herpes simplex virus infection

Background It has been shown that varicella zoster virus (VZV) and herpes simplex virus (HSV) can co‐localize to the same sensory ganglion. However, only a few case reports on VZV/HSV co‐infections exist. Objective To identify and characterize patients with concurrent VZV and HSV infection at the same body site. Subjects/Methods In 1718 patients, the presence of VZV and HSV in suspicious skin lesions was investigated by polymerase chain reaction analysis. Clinical characteristics of co‐infected patients were compared with matched control patients infected with either VZV or HSV. The data are discussed in the context of an extensive review of the literature. Results Twenty (1.2%) of 1718 patients were infected with both VZV and HSV at the same body site. The mean age was 54 years (range, 2–83). The clinical diagnosis was zoster in 65%, herpes simplex in 20%, varicella in 10% and erythema multiforme in 5% of cases. The trigeminus region was affected in 60% and the trunk in 25%. Involvement of the head was most commonly associated with a severe course of disease and with older age. Conclusion Simultaneous VZV/HSV infection is rare but can occur in immunocompetent patients, which is often overlooked. The majority of cases is localized to the trigeminus region and affects elderly people.     

Examination of non-involved skin, previously involved skin, and peripheral blood for herpes simplex virus DNA in patients with recurrent herpes-associated erythema multiforme

The association between infection with HSV and the subsequent, development of erythema multiforme is well established, although the role that the virus plays in the pathogenesis of this disorder is not known. HSV DNA has been detected in cutaneous lesions of herpes-associated erythema multiforme (HAEM), and it has been suggested that the tissue damage seen in these lesions is virus-specific. In the current, prospective study, we examined biopsies of lesional, non-involved, and previously involved but healed skin, in addition lo specimens of peripheral blood, from patients with HAEM, for HSV DNA by using the polymerase chain reaction. HSV DNA was detected in lesional skin of 10 of 11 patients compared to 2 of 11 non-involved skin biopsies obtained at the same time. I ISV was present in 4 of 6 blood specimens obtained during the acute episode. Five patients returned 3 months after the acute episode resolved for biopsies of previously involved skin. HSV was detected in 4 of these 5 biopsies. Thus, the presence of HSV DNA in the skin of pal inns with HAEM appears lo be predominantly in areas of clinical involvement; the virus remains in those cutaneous sites for up to 3 months without evidence of clinical disease; and HSV DNA may be detected in the peripheral blood cells during acute HAEM. Based on these findings, we suggest that the virus plays a role in lesion development, that the skin may function as a site of viral persistence, and that hemalogenous spread of viral DNA may bean important factor in the development of HAEM.     

Clearance of experimental cutaneous Staphylococcus aureus infections in mice

Staphylococcal skin infections are quite common in human patients. These infections often clear spontaneously, but may also progress locally and/or disseminate to cause serious and sometimes fatal deep infections. The present studies were undertaken to examine the clearance phase of experimental cutaneous Staphylococcus aureus infections in a mouse model system. Previous work in this system has shown that staphylococci applied to the skin rapidly disseminate to the spleen and kidney. In the present experiments the bacteria were found to persist at the skin infection site at a time (8 days after inoculation) when they had disappeared from the spleen and kidney. Examination of the infected skin at earlier times revealed rapid (within 6 h) invasion into the stratum corneum, stratum Malpighii, and dermis, but subsequent redistribution of bacteria (at 1–2 days) to more superficial sites, particularly crusts located just above the skin surface. The crusts seen in these infections were of two distinct types, which were termed type 1 and type 2. Type 1 crusts appeared first, consisted of bacteria, inflammatory cells, and debris, and developed over an intact epidermis. Type 2 crusts arose from the process of dermal necrosis previously reported to take place at 2 days in this model system. In the latter situation the bacteria were not really cleared from the epidermis and dermis; rather those layers were transformed into a superficial crust that contained the bacteria. Deep hair follicle infections in the dermis were found in these infections, but they did not persist and did not seem to be a reservoir for organisms in the dermis. Resolution of these experimental infections appeared to involve redistribution of invading bacteria to more superficial locations in crusts above the skin surface, marked proliferation of the epidermis, loss of the bacteria-laden crusts from the skin, and eventual healing of the cutaneous damage.