Detection of species – and tissue - unrestricted conformation – dependent tumor associated antigen(s) in immune complexes from plasma of tumor affected cattle and buffaloes
R Chopra, H Saxena
buffalo, cattle, conformational epitopes, immune complexes, tumor associated antigens
R Chopra, H Saxena. Detection of species – and tissue - unrestricted conformation – dependent tumor associated antigen(s) in immune complexes from plasma of tumor affected cattle and buffaloes. The Internet Journal of Veterinary Medicine. 2007 Volume 4 Number 1.
Rabbit hyperimmune serum against intact whole immune complexes from a mammary tumor affected dog gave positive reactivity in dot ELISA with plasma from cattle and buffaloes affected with various tumors compared to sera against the antigen – rich and the antibody – rich fractions of dissociated circulating immune complexes (CICs). These results suggest a possibility of existence of species – and tissue - unrestricted tumor associated antigens (TAAs) as conformation - dependent epitope(s) in CICs in bovine tumors.
Circulating immune complexes in tumor affected animals may be a rich source of tumor antigens capable of eliciting antibody response. The present study was aimed at exploring this possibility with blood plasma from tumor affected cattle and buffaloes.
Materials and methods
The present study was conducted on samples of blood plasma from 3 cattle and 6 buffaloes with histopathologically confirmed tumors of different kinds and from normal healthy animals.
Cattle tumors: The rabbit anti- whole IC serum gave a ++ reactivity with plasma samples of tumor bearing cattle and a + reactivity with plasma of normal healthy controls (Fig. 1; Table 1.).
Buffalo tumors: The rabbit anti- whole IC serum gave a +++ reactivity with 33.3% of the plasma samples and a ++ reactivity with 66.6% of the plasma samples of tumor bearing buffaloes and a + reactivity with plasma of normal healthy controls (Table 2.).
Cattle tumors: The rabbit anti- ICF1 serum gave the same (+) reactivity in all the samples of tumor bearing cattle as that of normal healthy controls (Fig. 1; Table 1.).
Buffalo tumors: The rabbit anti- ICF1 serum gave a ++ reactivity with 33.3% of the plasma samples of tumor bearing buffaloes while 66.6% of the plasma samples of tumor bearing buffaloes gave the same (+) reactivity as that of plasma of normal healthy controls (Table 2.).
In the present study, the rabbit hyperimmune serum against whole immune complexes from plasma of a dog with mammary tumor when tested against plasma of tumor affected cattle and buffaloes was found to give a low reactivity with plasma from tumor bearing cattle. In contrast, the reactivity was high with one third of the samples and low with two thirds of the samples of plasma from tumor bearing buffaloes. This difference in reactivity in only a proportion of samples within the same species may possibly be due to the different clinical stages and immunological status of tumor in different animals. However, the hyperimmune serum against the antigen – rich fraction I of the dissociated CICs gave a background reactivity comparable to the healthy controls in majority of the samples from animals with tumors in both, cattle and buffaloes.
Cronin et al. (1982) purified CICs from pleural effusions of patients with squamous and adenocarcinomas of lung. The hyperimmune sera raised against the antigen – rich portion of CICs were found to stain the tumors. The presence of TAAs in CICs has also been reported in melanoma patients by Gupta and Morton (1983). The antigenic portion of the dissociated complex was shown to react with allogeneic sera and with a rabbit anti-melanoma serum. Thus, positive reactivity of the plasma samples from tumor affected animals with serum against F1 fraction of CICs compared to the normal controls should indicate the presence of circulatory free antigen in the patients. However, the low positive reactivity with hyperimmune serum against F1 fraction of CICs observed in our study, may indicate an absence or a low level of circulating free antigen. The higher positive reactivity in case of anti-whole IC serum compared to anti-ICF1 or anti-ICF2 sera may possibly indicate the presence of conformational epitope(s) formed due to the antigen – antibody interaction which may be found in intact CICs but absent in circulating free antigen.
Chester et al. (1994) used monoclonal antibodies for the detection of free and immune complexed antigen in the sera of patients with colon carcinoma. They concluded that the analysis of both, IC bound and free circulating antigen, is a more sensitive indicator of the disease condition. In our study, the samples from tumor bearing bovines gave a negligible or background reactivity against the hyperimmune serum to ICF2 (antibody – rich) fraction of CICs comparable to that of healthy controls. The inability to detect tumor specific antibodies in plasma with these sera may possibly be due to the lack of humoral immune response against tumor antigens in these animals.
The present studies indicate that antibodies against the whole IC could detect the tumor associated antigen(s) in plasma of tumor affected bovines. The failure of antibodies to the antigen – rich and antibody – rich fractions of dissociated immune complexes to differentiate between plasma from tumor bearing and normal animals could possibly imply that the putative tumor associated antigen(s) may not exist as independent linear epitope(s). Instead, they may possibly exist as conformational epitope(s) formed by the binding of antigen and antibody. Such putative tumor marker(s) seem to be unrestricted to the tissue type and species concerned since the hyperimmune sera against CICs of dog with mammary tumor reacted with the plasma of cattle and buffaloes with various tumors.
Dr. H. M. Saxena, Flat no.9, First floor, Geetanjali Apartments, E – Block, Rishi Nagar, Ludhiana – 141001 India. Cellphone: +91-161-9417147813, Telefax (Res.): +91-161-2301315 E-mail: firstname.lastname@example.org