Effect of gonadotropin-releasing hormone vaccination on T lymphocyte changes in male rats

The aim of this study was to detect the effect of immunization against gonadotropin-releasing hormone (GnRH) on cell-meditated immunity. Three-week-old male Sprague-Dawley rats (n = 32) were randomly and equally assigned to two groups: 1) GnRH-tandem-ovalbumin immunized group; and 2) the control group (injected with an equivalent Al(OH)3 adjuvant). Blood samples were collected at two-week intervals to assess the level of GnRH-specific antibodies and testosterone. Moreover, blood and thymus samples were also collected to analyze the T lymphocyte subpopulations one and two months after the last booster immunization. T lymphocyte immunity against GnRH was activated during the first month post-immunization as exhibited by increased numbers of CD3+ (P < 0.05) and CD4+ (P < 0.05) T lymphocytes following testosterone suppression (P < 0.01), which was then restored and maintained at appropriate levels in the second month. In contrast, the differentiation of T lymphocytes in the thymus was reduced during the first month after immunization as exhibited by the significant decreased number of CD3+ (P < 0.05) cells, followed by the restoration and heightened numbers at later time points for both the number of CD3+ (P < 0.05) and CD4+ (P < 0.01) T lymphocytes. These results suggest that immunization against GnRH interferes with the number of lymphocytes during the early time points following immunization. The number of T lymphocytes initially decreased in the peripheral blood following immunization, but was replenished by newly exported cells from the thymus which eventually restored the T lymphocytes to normal levels.