Measurement of cell-mediated immunity against bovine papilloma virus by lymphoproliferative reactions

Leukocyte proliferation in vitro against cottontail rabbit papillomavirus in rabbits with persisting papillomas/cancer or after regression

Leukocyte proliferation responses to cotton-tail rabbit papillomavirus (CRPV) were measured in vitro with fresh whole blood as well as with ammonium chloride lysis-separated leukocytes. The antigens used were (1) CRPV particles produced in the athymic( (nu/nu) mouse xenograft system and (2) purified bacterial fusion proteins of the CRPV major and minor capsid proteins L1 and L2. CRPV-infected domestic rabbits with persistent papillomas or after papilloma regression, as well as uninfected controls were studied. There was a clearcut difference between infected and uninfected animals. We demonstrated antigen-specific leukocyte proliferation to at least one CRPV antigen in 12 of 21 infected rabbits but there was no positivity in 9 control animals (P = 0.004). There was whole-blood reactivity preferentially to intact CRPV particles in regressors. Specific but weak leukocyte proliferation against CRPV particles was detected in 6 of 9 regressor rabbits (66%) but only in 1 of 12 progressors (8%; P = 0.0158). This trend of greater reactivity to intact CRPV particles in regressors as compared with progressors was not seen with peripheral blood leukocytes isolated by ammonium chloride lysis. We conclude that specific leukoproliferative responses against capsid CRPV proteins exist in rabbits experimentally infected with CRPV.

Skin test to assess immunity against cottontail rabbit papillomavirus antigens in rabbits with progressing papillomas or after papilloma regression

This study analyzed in vivo antiviral cellular immune reactions in the Shope rabbit papilloma-carcinoma model. Antigens studied in experimentally infected domestic rabbits were cottontail rabbit papillomavirus particles produced with the athymic (nu/nu) mouse xenograft system and bacterial fusion proteins containing the major or minor capsid protein. Recall reactions to antigens were tested by classic intracutaneous tests. Positive reactions had a biphasic course. Histopathology of skin test biopsy specimens showed infiltrating polymorphonuclear cells during the early stages. Later they were replaced by predominantly perivascular infiltrates composed of mononuclear cells. Time course of swelling and infiltrates resembled a delayed-type hypersensitivity reaction. Ten of 11 regressor rabbits (p = 0.00006) and 10 of 20 progressors (p = 0.009) had positive skin tests with intact and/or denaturated virus particles and individual capsid proteins also could elicit specific skin reactions. Skin reactivity to the cottontail rabbit papillomavirus particles was also greater (p = 0.042) in regressor rabbits (8 of 11) when compared to progressors (7 of 20). Recall reactions remained detectable at post-regression times, ranging from several months up to more than 2 years. We conclude that specific skin reactions against the cottontail rabbit papillomavirus in infected domestic rabbits exist, and are strongly positive to intact particles of this papillomavirus in animals (regressors) clinically free of disease.

Langerhans' cells in equine cutaneous papillomas and normal skin

Langerhans' cells (LC) were investigated immunohistochemically and electron microscopically in normal equine epidermis and 133 equine cutaneous papillomas experimentally induced in five 2-year-old Thoroughbred horses. Class II major histocompatibility complex antigen-positive dendritic LC were found in the normal epidermis and ultrastructurally had the characteristic Birbeck's granules. In the developing phase of the papillomas, LC were significantly decreased in number and size, indicative of a hypofunctional state. In the regressing phase of the papillomas, LC were markedly increased in number, especially at the epidermis-dermis junction. LC with long dendrites were rich in cytoplasm with well-developed cytoplasmic organelles, including Golgi apparatus, lysosomes, Birbeck's granules, and multivesicular bodies. These LC were hyperfunctional. An infiltration of many T lymphocytes was also observed at the epidermis-dermis junction.

Antigen presentation and T-cell activation in epidermodysplasia verruciformis

Aberrant immune responses may play a role in the susceptibility of patients with epidermodysplasia verruciformis to human papilloma virus (HPV). We examined the stimulatory capacity of antigen-presenting cells from HPV-infected skin and peripheral blood T-cell responses of patients with epidermodysplasia verruciformis. The percentage of Langerhans cells in relation to total epidermal cells in suspension was slightly reduced in HPV-infected lesions, relative to apparently clinically uninfected epidermis. In addition, the morphologic appearance of Langerhans cells was altered in lesional epidermal sheets. Despite these abnormalities, Langerhans cells were functionally intact in their capacity to present alloantigens to T cells and, in fact, the epidermis of HPV-infected lesions demonstrated enhanced antigen-presenting activity in three of four patients tested. The antigen-presenting activity was entirely abrogated by removal of Langerhans cells and was not associated with increased activity of cytokines with stimulatory activity for the thymocyte co-stimulation assay. Although epidermodysplasia verruciformis T cells were unresponsive to autologous HPV-infected epidermis, they responded well to mitogens, allogeneic mononuclear leukocytes, and allogeneic epidermal cells. Epidermodysplasia verruciformis T cells were inhibited in their capacity to respond to allogeneic epidermal cells when they were simultaneously exposed to autologous epidermal cells from HPV-infected lesional epidermis, but not to normal-appearing epidermis. Thus, although Langerhans cell activity is intact in epidermodysplasia verruciformis, these individuals fail to respond to autologous papillomas, which may, at least in part, be explained by an interaction between papillomal epidermal cells and autologous T cells that results in an inhibited response.

Histopathological development of equine cutaneous papillomas

The histopathological development of equine cutaneous papillomas was studied in 78 warts naturally occurring in 50 one to 3-year-old Thoroughbred or Arab horses and in 54 warts experimentally induced in three 2-year-old Thoroughbreds. Lesions in the natural cases were categorized into three phases, growth, development and regression. Main lesions of the growing phase were marked hyperplasia of the basal cells and mild to moderate acanthosis, hyper- and parakeratosis with a few intranuclear inclusion bodies (IIB) which were positive with anti-bovine papillomavirus serum. In the developing phase, there was prominent acanthosis with cellular swelling and fusion, and marked hyper- and parakeratosis. Many IIB were also present in swollen or degenerative prickle cells and granular cells, with a high degree of parakeratosis in keratinocytes. In the regressing phase, epidermal layers were almost normal with only slight hyperplastic change. However, there was rete peg proliferation downward into the dermis with moderate proliferation of fibroblasts and collagen fibres. In addition, in 10 spontaneous and one experimental wart, the lesions were fibropapillomas and this has never been described in horses previously. It was concluded that papillomas were initiated by basal cell hyperplasia without viral antigen production, with formation of acanthosis and hyper- and parakeratosis with IIB production. These findings were confirmed by examination of the experimental cases on the basis of the gross diameter of the warts.