Mechanisms influencing activation and survival of normal and malignant lymphoid cells in the testis

Abstract

Acute lymphoblastic leukaemia (ALL) is the most common childhood malignancy and the testis is the third most common site of relapse after treatment. Testicular function is regulated by pituitary hormones, but the testicular microenvironment is also locally regulated through cell-cell interactions and by paracrine factors. Such factors could be of importance for the tendency for testicular relapse of ALL.

The aim of this thesis was to obtain a better understanding of the contribution of testicular paracrine factors to the tendency for relapse of treated childhood ALL.

Seminiferous tubules were shown to produce factors that inhibit lymphocyte proliferation in a stage related way. The characteristics of these factors indicate that they could be isoforms or multimers of bioactive transforming growth factor beta (TGFbeta). Seminiferous tubule extracts contain a factor that showed response in the CCL-64 mink lung epithelial cell line TGFbeta bioassay, indicating that the factor was TGFbeta. Neutralizing TGFbeta antibodies could reverse suppression of lymphocyte proliferation induced by testis protein extracts as further evidence that the activity is mediated by TGFbeta. TGFbeta dose-dependently inhibited rat testicular interleukin-1 (IL-1) driven proliferation in a mouse thymocyte IL-1 bioassay and polyclonal mitrogen stimulated rat PBL proliferation.

In co-cultures, Leydig cells suppressed polyclonal mitogen induced lymphocyte proliferation and suppressed recombinant IL-1alpha and IL-1beta as well as rat testicular IL-1alpha bioactivity in a mouse thymocyte IL-1 bioassay. The suppressive effect was not mediated by testosterone. A single injection of hCG induces a rapid surge of expression of pro-inflammatory cytokines in the rat testis. The reaction was not detectable in Leydig cell depleted rats, confirming that this inflammatory reaction is hormonally regulated and mediated via hypophyseal hormonal regulation of Leydig cells. As has been previously shown, this acute reaction can be mimicked by testicular injection of IL-1beta but not IL-1alpha.

IL-1beta was detectable in macrophages but not in Leydig cells after hCG dosing, indicating that Leydig cells can regulate inflammatory responses by activation of macrophages in the testis.

Using a rat leukaemia model and human leukaemic cells recovered from patients with childhood leukaemia, we could demonstrate that leukaemic cell proliferation can be regulated by testicular constitutive factors.

In conclusion, the present data suggest that testicular proteins can influence proliferation of normal as well as malignant lymphocytes. In the present study IL-1 and TGFbeta have been especially implicated - IL-1 as a proliferation-inducing factor and TGFbeta as a proliferation suppressive factor that might render malignant lymphocytes less sensitive to cytotoxic effects of chemotherapy. Production of such factors is, at least in part, under hormonal regulation by pituitary hormones. These results support a role for the testicular paracrine factors in the tendency for testicular relapse of ALL.