Anti-hCG immunization introduction

CONTRACEPTION

UJTJ-KG

II+IUNI~ATIO?J INTRODUCTION L.

P.

Tdwar

Anti-hCG--immunization is a potentially hopeful approach for development of an antipregnancy hCG is an early product of the trophovaccine. blasts and is believed to be crucial for sustenance of ovarian steroidogenesis without which pregnancy cannot be maintained in the major part ( 6to B The of the first trimester in the humans. weeks) hormone has to traval from the implanting blastoThe presence cyst to the ovaries through blood. of adequate amounts of antibodies in blood capable of binding with the hCG in a manner so as to neutralize effectively its biological activity can hCG can also interrupt the signal to the ovaries. have additional sites of action,e.g. at the placenta. Antibodies against hCG can be elicited in the humans by linking the molecule with a "foreign" carrier protein such as the tetanus toxoid (1). Biologically,the most effective antibodies neutralizing hCG action are generated by using the entire hCG. This is, however, not feasible owing to the likely production of cross-reaction with three other pituitary hormones (TSH, FSH, LH), which share a common subunit (alpha subunit) with hCG. The /!I-subunitsof the three pituitary and the placental hormones impart individuality to these The p-subunit of hCG is an adequate hormones. immunogen for formation of biologically effective antibodies (2, 3, 4). i3-hCG has large areas of homology in amino acid sequence with p-hLH, and can give rise to cross-reacting antibodies. The two hormonal subunits have however differences at 51 amino acid residues. Moreover the carbohydrate content of /3-hCG is also highei. An important question raised is whether these differences are adequate and are visualized immunologically. The present set of papers describes the properties of antibodies generated by the p-hCG based vaccine Pr-p-hCG-TT. Their avidity for binding with hCG and hLH and their. ability to interfere in the biological actions of the two hormones in various

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1978VOL.18N0.1

19

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in wivo and _in vitro systems are the subjects of -study. The dominant population of antibodies have higher Association Constants for hCG and neutralize preferentially its activity, in contrast to the reactivity of antibodies raised to entire gonadotropins. How frequently are LH cross-reacting antibodies formed ? Are such cross-reactions biologically relevant ? A concomitant issue posed and investigated is on the nature of immune complexes formed in immunized primates on challenge with hCG (& hLH), snd the degree of risk of deposits of such complexes in susceptible organs.

G.P. TALWAR

REFERENCES

20

1.

Talwar, G.P., Sharma, N-C., Dubey, S.K., Salahuddin, Me, Das, C., Ramakrishnan, 5.. Kumar, S. and Hingorani, VO : Isoimmunization against human chorionic gonadotropin with conjugates of processed D-subunit of the Proc. Natl. hormone and tetanus toxoid. Acad. Sci. 73: 218 (1976).

2.

Das, Cm, Salahuddin, He, and Talwar, 6.P.: Investigations on the ability of antisera produced by Pr-D-hCG-TT to neutralize the Contraception biological activity of hCG. 13: 171 (1976).

3.

Stevens, V.C. t Perspectives of development of a fertility control vaccine from hormonal In WHO antigens of the trophoblast. session Proceedings Symposium on Immunology Scriptor Copenhagen of Reproduction. (1976) p* 93.

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1978VOL.18 NO.1

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4.

Hearn,

J.P.

monkey

in

:

contraceptive Human National rd1.R.N.

1978

Its

of use

immunology.

Primates Prasad

VOL. 18 NO. 1

Academy, and

T.C.

In New Anand

the

in

in Biomedical

Science

(1077).

JULY

Reproduction

captivity:

marmoset

studies :

Use

of of

Research,

Indian

Delhi. Kumar,

NonEds.

p.

215