Dengue is a systemic viral infection transmitted to humans by the Aedes mosquitoes (Simmons et al., 2012). Infection by one serotype induces lifelong protection against homologous serotypes. A patient with the second infection with different serotypes have a higher risk of serious illness. The humoral and cellular immune profiles present after the first infection may not only fail to control the second infection with different serotypes but can also facilitate increased target cell infection and viral replication (Rothman, 2011).
Meanwhile, protection against other serotypes does not last long, and it does not provide cross-protection immunity. Other serotypes only provide temporary partial immunity. In endemic areas of dengue fever, a person can be infected by three other serotypes (Soegijanto, 1998). Therefore, multivalent to four serotypes is a necessity (Liu et al., 2008). Overall, the available data shows that PRNT50 titers alone are not enough to predict vaccine efficacy. Based on this paradigm, the dengue scientific community considers the role of T cells in protection against DENV (Lam et al., 2017).
METHOD AND RESULTS
White New Zealand rabbits (18 rabbits) were vaccinated using a multivalent dengue vaccine in different doses on day 0, and the booster was given on the 14th day. P0 is injected with PBS (control), P1 is injected 0.5 cc, and P2 is injected 0.3 cc. 200 μl of blood serum was collected on day 0, 7, 14, 21, and 28 for the isolation of peripheral blood mononuclear cell (PBMC). Observation of cellular immune responses from PBMC isolation was carried out by immunofluorescence using fluorescent microscopy to count TLR cell counts, CD4 + T cells, and CD8 + T cells.
The rabbits vaccinated with dengue multivalent showed a much higher number of TLR compared to the control group, although the results between P1 and P2 did not show a significant difference. Although there was a decrease in the number of TLRs on the 21st day (a week after the booster), and the TLRs increased again on the 28th day. The highest increase in TLR occurred on day 14 (several weeks after the first vaccination), while the highest number was reached on the 28th day. TLR receptors are considered important because TLR signals activate specific immune responses. They stimulate the production of transcription factors that produce various proteins and several cytokines that play a role in the immune system (Baratawidjaja et al.,2009). When there is an increase in the number of TLRs, activation of macrophages is more effective in identifying and capturing antigens, processing and then presenting them to T cell receptors for components of pathogenic viruses providing via TLR signal transduction and receptors for IFN-gamma.
Whereas for CD4 + T cells, although there was an increase in the number of cells consistently after vaccination in the group that was challenged and vaccinated, the P2 group on day seven did not show a significant difference (p> 0.05) when compared with the control group. On day 14 and day 28, P1 shows a significant difference to P2, whereas on day 21, P1 and P2 are not significantly different. The highest increase in CD4 + T cells and the highest number of CD4 + T cells occurred on day 28 (a few weeks after the booster was given).
Increased CD4 + T cells are in line with increased levels of immunoglobulins produced by rabbits after vaccination. It occurs because CD4 + T cells differentiate into plasma cells that can produce immunoglobulins. CD4 + T cells themselves also can differentiate into memory cells. Memory cells have an important role in the reintroduction of antigens quickly so that the levels of immunoglobulins formed will be higher. CD4 + T cells are estimated to control viral infections through a variety of mechanisms, including improved B cell, CD8 + T cells responses, production of inflammatory and anti-viral cytokines, cytotoxicity of virus-infected cells, and promotion of memory responses (Santet al., 2012).
The number of CD8 + T cells in the challenged and vaccinated group increased consistently after vaccination except in group P1 on day seven it did not show a significant difference (p> 0.05) with the control group. On the 14th and 28th days, P1 shows a significant difference with P2, whereas, on the 21st day, P1 and P2 are not significantly different. The highest increase in CD8 + T cells occurred on day 21 (a week after the amplifier), while the highest number of CD8 + T cells occurred on the 28th day. The virus is intracellular, so it activates CD8 + T cell receptors through the introduction of phagocyte cells. The protective role of T cells during viral infection is well known (Remakus et al.,2013). Recent evidence from mouse and human studies shows that T cells, especially the CD8 + subset, are very important mediators (Zellweger et al., 2014; Zellweger et al., 2015).
Based on this study, it can be concluded that 0.5 cc and 0.3 cc dose of dengue multivalent vaccines can increase the number of TLR, CD4 + T cells and CD8 + T cells against DENV in rabbits. A greater appreciation on the importance of T cells is also seen in recent vaccine developments that focus on assessing T cell activity in vaccinated individuals and animals (Weiskopf et al., 2015; Chu et al., 2015; Gil et al.,2016).
Author: Lita Rakhma Yustinasari, drh., M.Vet.
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Multivalent Dengue Vaccines and its Celluler Immune Response in New Zealand White Rabbit. US National Library of Medicine National Institute of Health
