ENCUESTA

The heterogeneity of the PLH subunit has been utilised in interspecies immunisations. Both passive and active immunisations have been done in a variety of species. Immunisation of males against LH affects LH-dependent androgen production in the Leydig cells. The efficacy of the immunisation is measured by its effect on the fertility of the animal, the size and weight of the testes and other accessory organs, testosterone levels in blood and histological changes in the testes, including changes in size and appearance of the Leydig cells and development of spermatogenesis (e.g. Wakabayashi and Tamaoki, 1966, Quadri et al., 1966). Table 1.3 summarises some of the experiments done by active immunisation against LH.

Early experiments done on rabbits, raising antibodies to purified sheep LH (ovine LH, oLH), showed that the antisera cross-reacted with pituitary preparations of a number of different species (Moudgal and Li, 1961). Rats passively immunised with anti-oLH sera showed signs of androgen deficiency, i.e. reduced size of the testes and accessory organs (Hayashida, 1963, Moudgal and Li, 1961).

Active immunisations of rats and rabbits with oLH in Freund’s complete adjuvant (FCA) also resulted in marked degenerative effects on the reproductive system. Although the antibodies cross-reacted with oFSH and oTSH specific effects due to the cross-reactivity were not observed (Quadri et al., 1966, Wakabayashi and Tamaoki, 1966). Effects on the testes show extensive variation between different experiments both in rats and in rabbits. An interesting phenomenon was recorded after immunisation of rabbits against bovine LH (bLH). There seemed to be thickening of the basement membranes of the tubules and proliferation of Leydig cells, suggesting an enhanced action o f LH rather than reduced (Pineda et al., 1967). This contrasts with other observations of LH immunised animals. An explanation might be that after successftil immunisation against LH androgen production in the testes is impaired and this lifts the androgen induced inhibition of LH synthesis in the pituitary and results in increased rather than reduced LH levels as seen after surgical castration.

LH conjugate response^ on T accessory sex glands

Rat oLH FCA all animals responded reduced atrophy and reduced weights Wakabayashi and Tamaoki, 1965

oLH none no response no efiFect no effect Wakabayashi and Tamaoki, 1965

oLH FCA * reduced reduced weight and azoospermie Awoniyi et al, 1989

Rabbit oLH FCA all animals responded reduced atrophy and reduced weights Wakabayashi and Tamaoki, 1965

oLH FCA all animals responded reduced azoospermie Jeyakumar et al, 1995

bLH FCA all animals responded * azoospermie Pineda et al, 1967

Dog pLH FCA varied reduced in responders reduced weight in responders Lunnen et al, 1974

Pig oLH FCA very varied no effect no effect Falvo et al, 1986

pLH-hSG FCA varied reduced reduced weight Falvo et al, 1986

Sheep pLH FCA dependent on amount o f pLH used reduced reduced weight Fahmy et al, 1999

Chimpanzee oLHp FCA response (1/1) * * Moudgal et al, 1985

Table 1.3

Some experiments looking at the affects of active immunisation against LH on the male reproductive system in mammals.

*It is noted if the response showed considerable variance between individual animals or if some did not respond at all *Not specified in reference.

oLH = ovine LH; bLH = bovine LH; FCA = Freund’s complete adjuvant; hSG = human serum globulin; T = testosterone.

i

General Introduction

The outcome o f immunisation against LH depends on the age of the animals when they are first immunised, whether they have reached puberty, are immature or mature adults (for a review see Wickings and Nieschlag, 1984). Passive immunisation using anti-LH antibodies in neonatal rats resulted in infertility for the remainder of their lives (Goldman et al., 1971). The effects of passive immunisations on adult animals were reversible. Rats passively immunised with anti-oLH antibodies showed severe androgen deficiency and subsequently a reduction in testes weight, atrophy of accessory organs such as the seminiferous vesicles, arrest of spermatogenesis and various histological changes (Hayashida, 1963). Active immunisation against LH shows similar changes in the reproductive system as after passive immunisation (Wakabayashi and Tamaoki, 1966). Testosterone levels in either passively or actively immunised rabbits were reduced, in some cases to castration levels. Libido and normal androgen-dependent behavioural patterns could be restored by testosterone replacement in immunised animals, although testosterone on its own was not always enough to restore normal spermatogenesis (Quadri et al., 1966).

The other gonadotrophins, FSH and hCG, have also been targeted as possible candidates for an anti-fertility vaccine, inducing a reversible change in the reproductive system for possible use in humans. Immunisation against FSH results in degenerative changes to the reproductive system similar to those seen after LH immunisations, although not to the same extent. Passive immunisation of immature rats with anti-FSH antibodies resulted in a decrease in testis weight, but had no effect on accessory glands and testosterone levels (Madhwa Raj and Dym, 1976). Results from active immunisations with FSH and passive immunisations with anti-FSH antibodies are very diverse, but in most cases some degenerative effects on spermatogenesis are found in immunised animals. Studies on monkeys have revealed that neutralisation of FSH by passive immunisation with anti-FSH antibodies causes reduced spermatogenesis due to regression of the germinal epithelium, proving that FSH is required for normal spermatogenesis (Wickings et al., 1980).

Human CG is produced by the placenta starting at the blastocyst stage of the embryo. Immunisation against hCG has therefore been viewed as a potential anti-fertility vaccine for women and extensive research has been done in that field, leading to clinical trials of three of the vaccines (reviewed in e.g. Talwar, 1997b). A major

drawback in using hCG, LH or FSH in an anti-fertility vaccine is the cross-reactivity found between antisera to one glycoprotein hormone with another hormone. The glycoprotein hormones all share various characteristics, besides having identical a

subunits. The p subunits on their own, or fragments of them, have therefore been used instead of the whole hormone.

Successful immunisation against LH results invariably in reduced androgen levels. Androgens affect not only spermatogenesis but also hbido and other male behaviour patterns. LH is therefore a prime candidate for an anti-fertility vaccine for use in male animals.