Research Journal of Biotechnology. 2014 Jan; 9(1): 53-56

Effect of Cyclophosphamide on the immune status of chickens vaccinated with Newcastle disease vaccine

Varalakshmi S.1* and Kirubaharan J. John2

1. Microbiology section, National Dairy Research Institute, Bangalore, INDIA

2. Microbiology section, TANUVAS, Chennai, INDIA

*vara_s@ymail.com

 

Abstract

The effect of Cyclophosphamide (CY) on the immune status of birds was studied by administering the chickens with live Newcastle disease vaccine. Normal and immune suppressed chickens were vaccinated with the Thermostable live Newcastle disease vaccine by ocular-nasal route at 10th day of age. The immune suppressed chickens had significantly low serum antibody titers and histopathological studies showed that there is depletion of bursal tissue in the CY treated chickens compared to CY untreated chickens. There is no significant difference in the cell mediated immunity between ablated and non ablated group. This study concludes that there is suppression of only humoral immunity by administering the cyclophosphamide and there is no effect on cell mediated immunity. CY will be used to study the role of cell mediated immunity and mucosal immunity in the absence of humoral immunity.

 

Supplement:

Cyclophosphamide (CY) is one of the immunosuppressive agents and it has been reported that CY induces a selective depletion of B lymphocytes leading to decreased antibody formation. Further CY has been used experimentally as an immunosuppressant to elucidate some aspects of the immune response such as the role of cell mediated immunity (CMI).

In chickens, both cellular and humoral immune responses were reported to play an important role in the host defense against Newcastle disease virus (NDV). In contrast to other paramyxoviruses, the protective role of CMI alone against NDV has been questioned and it has been reported that specific CMI response to ND by itself was not protective against challenge with virulent NDV. Conflicting reports are available regarding the serum antibody titre and the protective status of the bird against field infections. It is with these ideas this work was carried out to assess the protective role of CMI in the absence of humoral immune response.

In this study, the protective role of CMI response produced by field dose of different types of NDV vaccine was studied by suppressing the B cell response. For this, CY was administered in ovo and it was found to cause severe humoral immune deficiency when administered on days 16- 18 of incubation. Apart from suppressing humoral immune response by ablating the bursa of Fabricius, an attempt was also made to vaccinate birds with SDS treated NDV proteins. Treatment of NDV with SDS was done with an idea to damage the HN and F epitopes as these two proteins are responsible for attachment and entry of NDV into cells.

From the data generated in this study it is made clear that in the absence of humoral immune response, CMI response could not protect the chicks from virulent virus challenge. In all the trials, the CMI response was detected as early as 3rd day post vaccination and remains consistent up to the point of challenge. The probable reason for CMI not protecting birds could be due to the rapid multiplication of NDV inside cells that enables release of large amount of progeny virions quickly. In such a condition, it was unlikely that CMI response was sufficiently rapid to kill the virus infected cells and the neutralizing antibodies in circulation alone were found to neutralize the viruses. However, the role of CMI response should not be underestimated in limiting virus replication and it could be concluded that circulating neutralizing antibodies forming the key component of humoral immune response is the main response in limiting ND, perhaps supported by CMI response. This fact is further substantiated from results of trial, where the viral protein was treated with SDS and given as vaccine along with an adjuvant. Consequent to damage to conformational epitopes due to treatment with SDS, HI antibodies were identified in very low titers and none of the birds that received this vaccine survived the virulent virus challenge.

It could be observed from the data generated that development of humoral immune response was affected by the treatment with Cyclophosphamide (CY). However, it should be emphasized here that 100% depletion is not possible with CY and due to this reason, in trials in which birds received booster dose of vaccine, HI antibodies could be detected. Further 50% of the birds in these trials also survived the challenge. It should be noted here that in these trials , at the time of challenge all vaccinated birds had significant levels of CMI, but only 50% of birds, which had HI antibodies alone survived. This proves the fact that CMI alone is not protective against NDV infection in chickens.

 

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