**1. Introduction**

There is no doubt that human reproductive endocrine hormones display a handful of mysterious patterns in their ageing process. The patterns are debatable even among endocrinologists and physiologists alike. We did a secondary analysis of findings, to quantify part of the mysterious association, *of ageing process (surgical removal of endocrine uteri) and immune functions (HIV-risk) in non-gravid adult female humans*. Categorically, we asked ourselves whether there is any significant relationship between female reproductive endocrinology and HIV-pathobiology given the ageing process. We believe there is an unaccounted function(s) of reproductive hormones and HIV-pathogenesis in humans. Besides, the unknown function(s) seem(s) to function in a manner that is at present mysterious given the

current scientific knowledge base. We also considered the mystery to be descriptive to a number of other ageing related pathologies. The systemic reproductive endocrine mysteries reflect both structure and functions. At functional level, there exist frequent speculations, about mysterious benefits of endogenous progesterone (and even oestradiol?), against bacterial and viral invasions, along the reproductive tissues and cells. Otherwise, it is common knowledge in mammalian female embryology and anatomy, that during embryo-fetal development, premordial germ cells migrate, from the yolk sac to the gonadal ridge, and statistically populate the gonads. The movement is characterised by changes of the premordial germ cells into oogonia, in an unknown mechanism to science, even to the present day. Oogonia rearrange themselves into germ cell nests. These germ cell nests undergo a series of mitotic divisions. Oogonia enters 1st meiotic division as primary oocytes with arrest at diplotene stage until puberty. What exactly triggers those structural processes is still a mystery among scholars to date. The magic behind female mammalian reproductive endocrinology is not confined to structure.

There is palpable evidence to suggest that mammalian endocrine reproductive system is associated with a number of immune functions, some potentially beneficial against viral illnesses [1–4]. However, the concept of endocrine reproductive (dys)-functions against HIV infection in humans is only poorly understood [5]. For instance, Polis and colleagues have reported up to a 40% increased risk of HIV acquisition [6], associated with usage of progestin-based injectable contraceptives in adult females, specifically Depot Medroxy Progesterone Acetate (DMPA) [6]. However, much as the effects of potential confounding could not be completely ruled out in their study findings, it was still an interesting observation to our research group. Specifically, it followed logic, to check whether the same observation, was applicable to endogenous produced progesterone, in non-gravid state. Besides, most physiological functions of endocrine activities, and their effects on immune system, have been studied in adult males. Thus, the gap about the situation in adult females is widening, especially in the era of viral pandemics like SARS COV-2 and HIV/AIDS. It was on this basis, we hypothesised that *the female uterus, and its associated secretory functions, to be an important milieu, for enhancing HIV acquisition in humans*.

A number of actions displayed by female human reproductive system are associated with ageing process. For instance, it is still debatable among endocrinologists, on *how does the menstrual cycle coordinate itself*, *and cease to function after calendar time*, using hypothalamic-pituitary-gonadal axis. Besides, the uterine endometrium coordinates a handful of both reproductive and immunologic functions. Of importance to this chapter, uterine macrophages and epithelial cells have been shown to be key allies in mobilisation of innate defenses over calendar age [7, 8]. However, the exact cause behind the observation remains a matter of intellectual guess work among scientists to date. We hypothesized the observation to be related to probable endogenous progesterone and/or oestradiol effects.

Information on the relationship between gestation process in humans and HIVinfection is evident in published literature [9–14], and new information still accumulates rapidly [15–18]. Previous studies pinpointed potential biological mechanisms between endocrinology (i.e. endogenous oestradiol and progesterone effects) and immunobiology of HIV [4, 5]. However, most of this accumulated information tends to be biased due to samples used; characterised to be in gestational period, and therefore in an *altered physiologic state*. Little (if any) is known, about the contribution of endocrine functions, towards HIV-risk and HIV-disease process in normal

physiological states. To avoid biases associated with '*altered physiological processes*' prominent in gestational era, usage of non-gravid female humans, preferably after reproductive era, becomes justified.

There exists evidence about sex differences in immune responses among adult humans [1], but it is still not clear, the extent contributed by sex hormones, especially among adult female humans, in non-gravid state. We believe that, *there exists differential deleterious effects of female endogenous sex hormones, on HIV risks in non-gravid adult female human population*. However, to the best of our knowledge, the findings of this concept has not been evident in published literature to date.

Hysterectomy can simply be defined as *a surgical removal of the female uterus*. It can also include removal of adjacent structures (e.g. cervix) as evident in *total abdominal hysterectomy* and/or fallopian tubes and ovaries (*hysterectomy with (uni)-bilateral salpingo-oophorectomy*). Hysterectomy is the commonest gynaecologic surgery reported globally [19, 20]. We considered it as a natural surrogate equivalent of non-gravid state in our study cohort. Specifically, it offers a convenient platform, for analysing clinical and biological parameters associated with surgery, exclusively in non-gravid state. Effects of HIV on surgical indications and outcomes among women have been almost exclusively confined to Caesarean section. Caesarean section is an obstetric surgical procedure. Normal physiology in women, and their alterations in early stages of pathologic processes, can be best studied in non-gravid state. Thus, the quest for the interplay between female endocrine reproductive hormones (e.g. oestradiol and progesterone) and HIV pathobiology in non-gravid state remains unknown to the world of science. It was on this basis, we considered hysterectomised women as a natural reservoir to test our beliefs using a clinical research design and adopting specified statistical techniques in our hypothesis testing.
