Transitory disturbances in growing lactating rabbits after transient doe-litter separation

To determine the effect of a transient doe-litter separation (48 h) on milk production and feed intake from 1 to 21 days post-partum, a control group (C) in which litters had free access to nursing, and a biostimulated group (B) in which litters were separated from their does from d 9 to d 11 post-partum were used. Total milk production was higher in (C) than in (B) does (5090+/-1.1 g vs. 4593+/-150 g, P < 0.05). On days 12, 13, 14 and 15 of the lactation period, milk production was 40% (P < 0.0001), 18% (P < 0.05), 15% (P < 0.05), and 15% (P < 0.01) higher in (C) than in (B), respectively. No significant differences were observed in feed intake during the period studied (7961+/-352 g in (C) does, and 7834+/-329 g in (B) does). After fasting, 11-day-old kits showed lower gut weight, body weight, empty stomach relative weight (RW), stomach content RW and small intestine RW (P < 0.05), but the differences disappeared at 21 days of age. A reduction in villous height (P < 0.065) was observed in separated kits at 11 days old compared to 9- and 11 -day-old control kits (579.0+/-28.4 vs. 664.64+/-27.6, and 724.33+/-24.1 microm, respectively), but no differences were observed at either 16 or 21 days of age. Specific jejunal lactase activity increased significantly in 11-day-old separated kits (P < 0.05). A significant increase in sucrase activity at 21 days in both groups (P < 0.05) was detected. In conclusion, a fasting period of 48 h at 9 days of age does not compromise the subsequent development of certain digestive parameters of young rabbits.     

Susceptibility dynamics in neonatal BALB/c mice infected with Cryptosporidium parvum.

BALB/c Mice were infected as neonates and at different ages to study the susceptibility dynamics in this animal model to Cryptosporidium parvum. When 4-day-old animals were infected with 10(5) C. parvum oocysts, parasites were detected in the terminal ileum when the mice became 14-25 days old (10-21 days post-infection [PI]). The percentage of animals positive for parasites was 100% up to the age of 19 days (15 days PI) but decreased immediately thereafter until no parasites were detected in 26-day-old (22 days PI) or older mice. Parasite load also decreased in these animals from 184.7 parasites per high power field in 14-day-old animals (10 days PI) to 0.22 in 25-day-old (21 days PI) mice. In a second study, some neonatal mice became resistant to C. parvum when infection was attempted at day-10 of age (day-15 of age at sacrifice). The susceptibility to C. parvum decreased until 14 days of age (19 days of age at sacrifice) when mice could no longer be infected. Parasite load also decreased in infected mice from 235.6 parasites per high power field (9 days of age at sacrifice) to 0.25 (18 days of age at sacrifice).     

Adaptability of the digestive function according to age at weaning in the rabbit: II. Effect on nutrient digestion in the small intestine and in the whole digestive tract

The ability of young rabbits to digest a solid diet was evaluated according to the weaning age: 21 (W21, 12 litters) or 35 (W35, 12 litters) days of age. From 14 days onwards, the rabbits were fed the same pelleted feed. Three methods were compared to estimate the faecal digestibility in the young rabbits, between 24 to 28 and 38 to 42 days. Digestive balance at ileal and faecal levels was determined for the main nutrients provided by milk and solid feed. The W21 rabbits increased their solid feed intake only 2 days after their weaning, when compared with suckling rabbits. Thus, their crude protein (CP) intake remained lower until 26 days compared with the W35 rabbits (from 41%, P < 0.01), as well as their crude fat intake until 28 days (from 72%, P < 0.001). On the contrary, the W35 rabbits increased their solid feed intake without a delay after weaning, quickly reaching the intake level of the W21 rabbits. The amounts of organic matter (OM) and CP reaching the caecum were increased on day 28 by 56% and 42% in the W21 rabbits compared with the W35 rabbits, respectively (P < 0.05), and were similar between groups on day 42. Starch ileal digestibility coefficients were 94·2% and 95·4% in 28- and 42-day-old rabbits, respectively, irrespective of the weaning age. The amount of starch flowing through the ileo-caecal junction was low and only tended to be higher on day 28 in the W21 group (0.20 v. 0.15 g/day in the W35 group, P = 0.10). The digestive balance pointed out that the digestible energy intake was similar between weaned and suckling rabbits from 23 to 27 days, a phenomenon partly explained by a high ability of the W21 rabbits to digest starch (98%) and NDF (36%). Indeed, the amounts of starch and NDF digested by the W21 group were 2.0- and 2.4-fold higher than those of the W35 rabbits at this period (P < 0.001). However, they ate 20% less digestible proteins than still-suckling rabbits (P < 0.001). From 38 till 42 days, only a lower ability of the W21 rabbits to digest lipids was detected (P < 0.05). In conclusion, early-weaned rabbits were able to adapt quickly to digest large amounts of starch and fibres.     

不同年龄昆明白小鼠卵母细胞的生发泡互换

为探讨卵母细胞减数分裂异常及其与年龄相关变化之间的关系,对不同年龄段昆明白小鼠卵母细胞进行了生发泡(GV)移植研究。应用显微操作和电融合技术,将6~8周龄小鼠GV期卵母细胞分别与6月龄9、月龄和12月龄小鼠GV期卵母细胞进行GV互换,所形成的6种GV-胞质体复合体的融合率(89.7%~95.6%)和6种重组卵母细胞的成熟率(83.5%~88.2%)并不因小鼠年龄的改变而有所变化。成熟的6种重组卵母细胞经体外受精后,形成原核期胚和2-细胞期胚的比率(分别为80.0%~87.3%和42.7%~50.9%)并不因不同年龄小鼠卵母细胞GV互换所带来的细胞质或细胞核的改变而受到影响。     

Vertical transmission of Neospora caninum in BALB/c mice determined by polymerase chain reaction detection.

Vertical transmission of Neospora caninum was evaluated in BALB/c mice using an N. caninum-specific polymerase chain reaction (PCR) assay as a means of detecting parasite transmission to offspring. BALB/c mice were infected with the NC-1 isolate of N. caninum during pregnancy (days 8-15 gestation). Transmission of parasite, detected by PCR, was determined in 2- to 23-day-old offspring. When dams were infected on days 13-15 of gestation, transfer of parasites was detected in only a proportion of the litter. Infection between days 8 and 12 of gestation resulted in a high frequency of parasite transmission; every offspring from all litters was infected. The tissue locations of parasites in pups of different ages were determined. In young pups (2- to 4-days-old), the predominant sites of infection were the lungs and the brain. In older pups (7- and 23-days-old) the predominant site of infection was the brain. This study shows that PCR may be useful for evaluation of candidate vaccines against horizontal N. caninum infection, vertical transmission, or both.     

Sexual maturation of male <Emphasis Type="Italic">Bactrocera correcta</Emphasis> (Diptera: Tephritidae) and age-related responses to β-caryophyllene and methyl eugenol

Sexual maturation of male Bactrocera correcta (Bezzi) and age-related responses to β-caryophyllene (CP) and methyl eugenol (ME) were examined to identify effective attractants for sexually immature males of the species. Sexual maturation rates (100 × number of cages containing males which attained sexual maturity/total number of cages at a given day) over different ages were 0.0%, 6.7%, and 100.0% for 5-, 6-, and 13-day-old, respectively, and at all the different ages, more males were captured with CP than with ME. The capture rate (the predicted probability by logistic regression) with CP was 29.7% (30.6%) for 5-day-old males, which were still sexually immature, and 52.7% (38.2%) for 6-day-old males, for which the earliest sexual maturation was observed. In contrast, no 5-day-old males responded to ME (the probability was 12.6%), and the capture rate (the probability) of 6-day-old males was merely 0.3% (14.5%), while the rate gradually increased later. The present study revealed that certain males of B. correcta responded to CP prior to sexual maturation but not to ME under the laboratory conditions. These results imply that CP could be an effective attractant used in male annihilation techniques for B. correcta and that ME may not be useful.     

Effects of age and parity on litter size and offspring sex ratio in golden hamsters (Mesocricetus auratus)

Golden hamsters that were mated repeatedly from 55 days of age produced 6-12 litters. Litter size at birth rose between the 1st and 2nd litters, peaked on the 3rd, and declined steadily after the 5th litter. Offspring sex ratio (% male) at birth followed a similar pattern: increasing between the 1st and 2nd litters, remaining high through the 3rd, and becoming increasingly female-biased thereafter. Weaning success decreased sharply after the 6th litter and most dams failed to raise any young to weaning after the 9th litter. These sequential effects on litter size, offspring sex ratio and weaning success were also observed in females mated once at different ages, but they occurred considerably later in life, i.e. increasing parity hastened the effects of advanced age. These age- and parity-related changes in litter composition are consistent with the Trivers-Willard hypothesis that physiologically-stressed females would skew offspring sex ratios to favour daughters. However, since the observed changes in sex ratio were probably due to differential prenatal mortality, their adaptive significance is unclear.     

Reproductive performance of multiparous rabbit lactating does: effect of lighting programs and PMSG use

This study aims to determine if Pregnant Mare Serum Gonadotrophin (PMSG), used for oestrous synchronization in multiparous lactating does, could be replaced by one of the following lighting schedules without impairing reproductive performance: (a) 12-h L (light)/12-h D (dark) or (b) 8-h L/16-h D, until day 6 before artificial insemination (AI), when in both cases photoperiod was changed to 16-h L/8-h D and maintained until the day of AI, and in the following 4 days post Al the light hours were progressively reduced to the initial schedules. Two groups of 20 does each were respectively submitted to one of the lighting schedules specified above. All does were artificially inseminated in 6 consecutive cycles at 42 days intervals. In the first, third and fifth AIs, PMSG (20 IU/doe via sc 48 h before AI) was used in the two groups of does, whereas in the second, fourth and sixth Als no hormonal treatment was used. Degree of oestrous synchronization (also referred in text as sexual receptivity) was estimated by the colour of the vulva at AI. Reproductive performance of does was evaluated based on fertility (kindling rates), prolificity, mortality at birth, mortality at 21 days post birth, weight of the litter at 21 days post birth and number of weaned rabbits. Oestrous was better synchronized when PMSG was used with any of the two lighting programs. Without using PMSG, a photoperiod of 12-h L/12-h D until 6 days before AI resulted in a better sexual receptivity of does than 8-h L/16-h D. Fertility, prolificity, mortality of young rabbits at 21 days, the weight of the litters at 21 days and the number of weaned rabbits did not vary with the lighting program and were not affected by the PMSG treatment. Mortality at birth, however, was higher (+1 dead kit per litter) in litters housed under a light program of 12-h L/12-h D. Global productivity (number of weaned rabbits per 100 inseminated does) was better when using PMSG, for both lighting schedules. When using a photoperiod of 12-h L/12-h D until 6 days before AI, and omitting the PMSG treatment, global productivity was scarcely reduced, however, it was considerably impaired when using a photoperiod of 8-h L/16-h D until 6 days before AI and no PMSG treatment.     

Postnatal development of vascularity in the inferior colliculus of the young rat

The inferior colliculus in the rat midbrain is an auditory relay center whose functional maturation occurs postnatally. We examined by morphometry the vascularity and the nuclear profile density of the inferior colliculus in normal young rats at different ages (before and after the onset of auditory input). We also compared this region with a frontal region of the cerebral cortex in 24-day-old rats. The inferior colliculus from aldehyde-perfused Sprague-Dawley rats aged 5, 9, 14, and 24 days was analyzed by light microscopy of semithin plastic sections. The central region (mostly the central nucleus) was sampled at 5 levels representing its entire rostrocaudal extent. Patent-blood-vessel profiles were counted and classified according to their size and profile orientation. Counts of nuclear profiles in the same sections were also made. In the inferior colliculus of rats between 5 and 24 days of age, the small (less than 10-microns diameter) cross-sectioned vessel profiles increased over 6-fold in number per unit area. Correspondingly the vascular volume density, estimated by differential point counting, increased between these ages. However, there was a decrease in the number of neuronal and glial nuclear profiles per unit area, probably because of growth in the volume of the neuronal perikarya and processes, along with cell emigration reported to occur at early postnatal ages. This study has shown that an increase in vascularity in the central region of the rat inferior colliculus continues for up to 2 weeks after the onset of hearing.(ABSTRACT TRUNCATED AT 250 WORDS)     

Kin Recognition and Maternal Care under Restricted Feeding in House Mice (Mus domesticus)

This study tests the hypothesis that female house mice (F1 generation of wild caught Mus domesticus) should preferentially invest in own offspring if confronted with young of different degrees of relatedness. The maternal behaviour of females with litters of 4 own and 4 unrelated alien young (cross-fostered at day 1 of lactation) was analysed during a lactation period of 22 days both under ad libitum and under restricted feeding (food was restricted by 20%). Cross-fostering and restricted feeding had no effect on the amount of time spent nursing until weaning. Under both feeding conditions the females did not differ in their maternal behaviour towards own and alien young: there were no significant differences either in the amount of time spent nursing own versus alien pups or in the time spent licking own versus alien young. Weight gain of own and alien = wild littermates did not differ significantly in mixed litters and was similar both under ad libitum and under restricted feeding. Such indiscriminate behaviour might be adaptive if female house mice prefer to communally nest with a relative and thus improve their inclusive fitness by investing in own and related offspring in a communal nest. Under moderate restricted feeding females could not wean the entire litter but reduced litter size by cannibalizing on average 2.7 pups (75% of the pups were killed when they were 4–8 days old). Females with cross-fostered litters killed as many own as alien young. This suggests that females cannot discriminate between own and unrelated young if cross-fostering takes place at day 1 of lactation. Besides testing kin recognition abilities, the experiments also allow analysis of the weaning strategy of females under food shortage. Under restricted feeding, body weight of the females was significantly lower during middle lactation than under ad libitum feeding. Weaning weight of young in reduced litters under food restriction (9–10 g) did not differ significantly from weaning weight of young in litters of 7–10 young, but was lower than that of young in similar sized litters (litter size 6), under ad libitum feeding. The maternal behaviour of cannibalizing some young under food shortage can be interpreted as a weaning strategy which results in the largest number of offspring that can be raised to a minimal weaning weight of 9–10 g. Such a weaning strategy might represent a favourable trade-off between number and size of young produced.     

An early stimulation of solid feed intake slightly influences the morphological gut maturation in the rabbit

The impact of dietary factors on the gut morphological maturation is poorly documented in rabbits. The weights of the digestive segments as well as the morphology of villi and crypts along the small intestine were analysed weekly from day 14 till day 49, in two rabbit groups weaned at either 21 (W21 group, n = 12 litters) or 35 days (W35 group, n = 12 litters) of age. From 21 till 35 days, the W21 group ate 57% more solid feed than the W35 group (P < 0.01), and presented slighter body weights from day 28 till day 49 (-9%, P < 0.05). Tissue weights of the empty digestive segments, as expressed relative to the body weights, were higher in the W21 than in the W35 group from day 28 till day 49 (P < 0.001), whereas absolute tissue weights appeared similar (except for the proximal colon). From day 28 to day 49, small intestinal villi grew in height and surface area (P < 0.05) whereas the crypts deepened. Villous height followed a proximo-distal decreasing gradient from the duodenum to the ileum (P < 0.05) from day 28 onward. The villous height to width ratio changed with the beginning of significant solid feed intake: from a thin shape until day 21, villi became wider from day 28 on. The effect of weaning age on mucosal morphology was insignificant, except for the jejunal crypts whose surface area and depth were higher in the W21 group. The present results showed that morphological changes in the digestive tract of young rabbits were weakly influenced by an early stimulation of solid feed intake.     

Capacity of mouse oocytes from preantral follicles to undergo embryogenesis and development to live young after growth, maturation, and fertilization in vitro

A system is described here by which live mice can be produced from oocytes isolated from 12-day-old mice, be grown, matured, and fertilized in vitro, and then be transferred to pseudopregnant females. These oocytes were, at the time of isolation from preantral follicles, in about mid-growth phase and incompetent of undergoing germinal vesicle breakdown (GVB) without further development. The developmental competence of mouse oocytes that grew and underwent maturation in vitro was compared to oocytes that grew in vivo and underwent maturation in vitro. After isolation from mice 16 through 28 days old, oocytes were found to increase in size and to sequentially acquire the ability to undergo GVB, produce a polar body, cleave to the 2-cell stage after insemination, and develop to the blastocyst stage. Moreover, the number of cells per blastocyst increased with the age of the mice from which the immature oocytes were isolated. Oocyte-granulosa cell complexes isolated from 12-day-old mice were cultured for 10 days. At the end of the culture period, the oocytes had grown to a size equivalent to oocytes isolated from 16-day-old mice, and 87% of the in-vitro-grown (IVG) oocytes underwent GVB; 79% of these produced a clearly visible polar body when maturation occurred in the presence of follicle-stimulating hormone (FSH). The IVG oocytes cleaved to the 2-cell stage after insemination in vitro with a frequency equivalent to superovulated ova and ova that matured in vitro after isolation from 22-day-old mice.(ABSTRACT TRUNCATED AT 250 WORDS)     

Teratogenic potential of inhaled carbon monoxide in mice and rabbits.

Pregnant CF-1 mice and New Zealand rabbits were exposed to carbon monoxide at a concentration of 250 ppm for 7 or 24 hours daily during the period of major organogenesis, days 6 through 15 of gestation in mice and 6 through 18 of gestation in rabbits. Carboxyhemoglobin levels in the range of 10--15% were observed in both species (control animals had 0.7% or less). Carbon monoxide was not found to be teratogenic in either species. In mice, a significant increase in the incidence of some minor skeletal variants was observed. One litter in each of the carbon monoxide-exposed groups of mice was completely resorbed; none of the litters of control mice or of control or exposed rabbits were completely resorbed. The fetuses of mice exposed to carbon monoxide for seven hours daily were heavier than control fetuses, and those exposed for 24 hours daily were lighter than control fetuses. The reason for this result is not known.     

Selected aspects of collared peccary (Dicotyles tajacu) reproductive biology in a captive texas herd

Collared peccaries (Dicotyles tajacu) from 32 litters were born in captivity during the period from September, 1981 through July, 1983. Incidence of singleton, twin, and triplet litters was 28%, 66%, and 6%, respectively. Mean (± SE) weight of young from singleton, twin, and triplet litters was 751 (± 35) gm, 698 (± 17) gm, and 612 (± 74) gm, respectively. Sex ratio among all litters was 56:44 (M:F). Neonatal mortality amounted to 9% of the young born. Mean duration of estrus was 2.60 days and mean length of gestation was 145.6 days. Evidence indicated that multiple copulations increased ovulation rate and the chance for conception.     

Population biology of small mammals in Pureora Forest Park .2. The feral house mouse (

Over five years from November 1982 to November 1987, we examined 395 mice collected from unlogged and logged native forest and from exotic forest at Pureora Forest Park, in the central North Island of New Zealand. Sex ratio, litter size, and breeding effort (pregnancy rate in females, proportion of males with visible tubules) were similar in all samples. By contrast, both density (captures per 100 trap-nights = C/ 100TN) and recruitment (proportion of young mice of age classes 1-3) were higher in densely vegetated habitats (along the road edge or in a young exotic plantation) than in the forest interior, whether logged or not. The age structures of the road edge and interior forest samples were significantly different (road edge, 33-35% young; interior, 10-11% young, means adjusted for sex, season and year by GLM). Mice of a given age caught in summer were larger, especially the females, implying that young mice grew faster in summer than at other seasons, and that older mice, especially females, also put on extra weight in summer. Most pregnant mice were found in spring and summer, but there was no winter quiescence in mature mice of either sex, and three of 29 pregnant females were collected in August. In five of 29 litters of embryos, at least one embryo was resorbing, totalling 12 of 161 embryos (7.4%). Litter size (viable embryos only) ranged from 5 to 8 (average 6) in 23 spring and summer pregnancies, but only 1-5 in four autumn and winter pregnancies. At high densities during 1984 in the young plantation (41.1 C/100TN in May) mice were significantly smaller in autumn, though somewhat larger in spring, and fewer young were recruited in 1984 and 1985. In these years we found significantly fewer males fertile, litters smaller and pregnancy rates lower, both in the plantation and in other habitats. The population Peak was much higher than most apparently similar post-seedfall Peaks in beech forest documented by the same methods, but it was different because (1) it developed very suddenly in autumn rather than building up slowly over winter and spring and Peaking in summer; (2) it was not preceded by winter breeding; and (3) it was made up mostly of mice born in the previous summer, whereas Peak populations in beech forests are usually made up of mice born during the previous winter and spring.     

Effect of acute altitude hypoxia on fatty acid proportion in the plasma of rats of different ages

Using gas chromatography, the authors studied the development of the proportion of 25 saturated and non-saturated fatty acids in the plasma of Wistar rats of their own breed aged 5, 10, 14 and 25 days and adult (both sexes), and in three age groups (5 and 14 day and adult) they determined the effect of acute altitude hypoxia. Fatty acids were determined as methylesters (FAME) (Base 1978), using the method already described by Smídová et al. (1984a), in mixed blood plasma obtained from decapitated control and experimental animals. Altitude hypoxia, which corresponded to 9 000 m, lasted 20 min. The temperature was kept stable at 25 degrees C. Marked changes occurred during ontogenesis in the proportion of total fatty acids (TFA) in the plasma; the proportion of sigma non-saturated FA fell significantly during maturation, chiefly in favour of monoene FA, with a resultant significant drop in their reciprocal index (sigma saturated/sigma monoene). The proportion of all saturated FA amounted in 5-day-old rats to 54% of the total quantity, but in adult rats to only 40%. Acute hypoxia had a demonstrable effect in all three age categories. In 5-day-old rats it led to significant changes in 7 FA and in adult rats in 10. In both 5-day-old and adult animals it produced an increase in the arachidonic acid level. The results are discussed in relation to previous findings on the effect of the same hypoxia on FA proportion in various parts of the CNS of rats of different ages.     

Defensins play a crucial role in protecting mice against oral Shigella flexneri infection

An earlier study revealed that 4-day-old mice, but not older mice, were infected with invasive Shigella strains. Here we attempted to determine the underlying mechanism that induces inflammation in the intestines of neonate mice after oral Shigella infection. Wild-type BALB/c mice of different ages (7, 14, and 35 days old) were orally administered GFP-expressing Shigella flexneri 5a M90T strain (5 × 10⁹ CFU) and analyzed for colonization 6 h following infection. We found that Shigella localized in the epithelium, lamina propria, and crypt regions of the small intestines of 7-day-old BALB/c mice. Microarray analysis revealed that expression levels of cryptdin and various types of cryptdin-related mRNA (e.g., cryptrs-2, -5, -7, -12 and lysozyme) in the small intestines were significantly lower in 7-day-old than in older mice regardless of Shigella infection status. Interestingly, matrix metalloprotease-7 (matrilysin)-deficient (MAT^−/−) mice of B6 background had more colonies and more severe symptoms of inflammation in the intestines than did wild-type B6 mice after oral Shigella challenge. This suggests that cryptdin-related antimicrobial molecules are indispensable for efficient protection against oral Shigella infection.     

Demonstration of a macrophage migration enhancement factor in the sera of young rabbits

Alveolar macrophages (AM), harvested from the lungs of untreated normal young rabbits (New Zealand White) 14 days to 8 weeks of age, exhibited a state of migration stimulation compared to AM from normal adult rabbits (5 to 6 months of age). Migration of AM from normal adult rabbits (New Zealand White) was stimulated 2.0- to 2.5-fold when incubated with sera from 39- to 46-day-old rabbits compared with sera from normal adult rabbits. Furthermore, 4-day spleen cultures obtained from animals 28 to 59 days of age yielded supernatants that also stimulated the migration of adult AM. The spleen cell culture supernatants from 42- to 49-day-old animals had the greatest activity and stimulated the migration of adult AM 2.5- to 3.2-fold compared to the supernatants from adult normal rabbits. The peak production of migration enhancement factor (MEF) by splenic lymphoid cells coincided with the peak activities found in the sera. It was observed that nonadherent peanut agglutinable lymphoid cells produced MEF. When sera or culture supernatants containing MEF were mixed with MIF-containing adult sera or spleen cell culture supernatants, the respective activities were neutralized. The large migrations of normal neonatal AM were diminished by the addition of MIF-containing sera obtained from BCG-sensitized/challenged rabbits. In contrast, AM from BCG-sensitized rabbits, which exhibited a state of reduced migration, were enhanced by MEF-containing sera from untreated young rabbits. Three peaks of MEF activity were detected in Sephadex G-100 column fractionated sera from 42-day-old rabbits having MWs of approximately (Peak I) 80,000, (Peak II) 43,000, and (Peak III) 8000 to 18,000; most of the activity was found in peaks II and III. Two peaks of MEF activity were detected in Sephadex G-100 column-fractionated spleen cell culture supernatants from 42-day-old rabbits having MWs of approximately (Peak I) 35,000 to 43,000 and (Peak II) 10,000 to 14,000; most of the activity was in peak I which corresponds to peak II of the serum fractionation experiment. Collectively, these data indicate that MEF is a lymphokine that could be important in the modulation of cell-mediated immune effector responses.